platform/x86: alienware-wmi: fix format string overflow warning

gcc points out a possible format string overflow for a large value of 'zone':

drivers/platform/x86/alienware-wmi.c: In function 'alienware_wmi_init':
drivers/platform/x86/alienware-wmi.c:461:24: error: '%02X' directive writing between 2 and 8 bytes into a region of size 6 [-Werror=format-overflow=]
   sprintf(buffer, "zone%02X", i);
                        ^~~~
drivers/platform/x86/alienware-wmi.c:461:19: note: directive argument in the range [0, 2147483646]
   sprintf(buffer, "zone%02X", i);
                   ^~~~~~~~~~
drivers/platform/x86/alienware-wmi.c:461:3: note: 'sprintf' output between 7 and 13 bytes into a destination of size 10

This replaces the 'int' variable with an 'u8' to make sure
it always fits, renaming the variable to 'zone' for clarity.

Unfortunately, gcc-7.1.1 still warns about it with that change, which
seems to be unintended by the gcc developers. I have opened a bug
against gcc with a reduced test case. As a workaround, I also
change the format string to use "%02hhX", which shuts up the
warning in that version.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81483
Link: https://patchwork.ozlabs.org/patch/788415/
Suggested-by: Andy Shevchenko <andy@infradead.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[andy: added empty lines after u8 zone; definitions]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/alienware-wmi.c

@@ -255,12 +255,13 @@ static int parse_rgb(const char *buf, struct platform_zone *zone)
 
 static struct platform_zone *match_zone(struct device_attribute *attr)
 {
-	int i;
-	for (i = 0; i < quirks->num_zones; i++) {
-		if ((struct device_attribute *)zone_data[i].attr == attr) {
+	u8 zone;
+
+	for (zone = 0; zone < quirks->num_zones; zone++) {
+		if ((struct device_attribute *)zone_data[zone].attr == attr) {
 			pr_debug("alienware-wmi: matched zone location: %d\n",
-				 zone_data[i].location);
-			return &zone_data[i];
+				 zone_data[zone].location);
+			return &zone_data[zone];
 		}
 	}
 	return NULL;
@@ -420,7 +421,7 @@ static DEVICE_ATTR(lighting_control_state, 0644, show_control_state,
 
 static int alienware_zone_init(struct platform_device *dev)
 {
-	int i;
+	u8 zone;
 	char buffer[10];
 	char *name;
 
@@ -457,19 +458,19 @@ static int alienware_zone_init(struct platform_device *dev)
 	if (!zone_data)
 		return -ENOMEM;
 
-	for (i = 0; i < quirks->num_zones; i++) {
-		sprintf(buffer, "zone%02X", i);
+	for (zone = 0; zone < quirks->num_zones; zone++) {
+		sprintf(buffer, "zone%02hhX", zone);
 		name = kstrdup(buffer, GFP_KERNEL);
 		if (name == NULL)
 			return 1;
-		sysfs_attr_init(&zone_dev_attrs[i].attr);
-		zone_dev_attrs[i].attr.name = name;
-		zone_dev_attrs[i].attr.mode = 0644;
-		zone_dev_attrs[i].show = zone_show;
-		zone_dev_attrs[i].store = zone_set;
-		zone_data[i].location = i;
-		zone_attrs[i] = &zone_dev_attrs[i].attr;
-		zone_data[i].attr = &zone_dev_attrs[i];
+		sysfs_attr_init(&zone_dev_attrs[zone].attr);
+		zone_dev_attrs[zone].attr.name = name;
+		zone_dev_attrs[zone].attr.mode = 0644;
+		zone_dev_attrs[zone].show = zone_show;
+		zone_dev_attrs[zone].store = zone_set;
+		zone_data[zone].location = zone;
+		zone_attrs[zone] = &zone_dev_attrs[zone].attr;
+		zone_data[zone].attr = &zone_dev_attrs[zone];
 	}
 	zone_attrs[quirks->num_zones] = &dev_attr_lighting_control_state.attr;
 	zone_attribute_group.attrs = zone_attrs;
@@ -481,12 +482,13 @@ static int alienware_zone_init(struct platform_device *dev)
 
 static void alienware_zone_exit(struct platform_device *dev)
 {
+	u8 zone;
+
 	sysfs_remove_group(&dev->dev.kobj, &zone_attribute_group);
 	led_classdev_unregister(&global_led);
 	if (zone_dev_attrs) {
-		int i;
-		for (i = 0; i < quirks->num_zones; i++)
-			kfree(zone_dev_attrs[i].attr.name);
+		for (zone = 0; zone < quirks->num_zones; zone++)
+			kfree(zone_dev_attrs[zone].attr.name);
 	}
 	kfree(zone_dev_attrs);
 	kfree(zone_data);