hwmon: (it87) Add missing sysfs attribute group terminator

Attribute array it87_attributes_in lacks its NULL terminator,
causing random behavior when operating on the attribute group.

Fixes: 52929715634a ("hwmon: (it87) Use is_visible for voltage sensors")
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: stable@vger.kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/it87.c

@@ -2015,6 +2015,7 @@ static struct attribute *it87_attributes_in[] = {
 	&sensor_dev_attr_in10_input.dev_attr.attr,	/* 41 */
 	&sensor_dev_attr_in11_input.dev_attr.attr,	/* 41 */
 	&sensor_dev_attr_in12_input.dev_attr.attr,	/* 41 */
+	NULL
 };
 
 static const struct attribute_group it87_group_in = {