platform/x86: panasonic-laptop: constify attribute_group structures.

attribute_groups are not supposed to change at runtime. All functions
working with attribute_groups provided by <linux/sysfs.h> work
with const attribute_group. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   2505	    600	      4	   3109	    c25	drivers/platform/x86/panasonic-laptop.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   2569	    536	      4	   3109	    c25	drivers/platform/x86/panasonic-laptop.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

drivers/platform/x86/panasonic-laptop.c

@@ -437,7 +437,7 @@ static struct attribute *pcc_sysfs_entries[] = {
 	NULL,
 };
 
-static struct attribute_group pcc_attr_group = {
+static const struct attribute_group pcc_attr_group = {
 	.name	= NULL,		/* put in device directory */
 	.attrs	= pcc_sysfs_entries,
 };