PM / devfreq: 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
621 176 0 797 31d drivers/devfreq/governor_userspace.o

File size After adding 'const':
text data bss dec hex filename
670 144 0 814 32e drivers/devfreq/governor_userspace.o

Signed-off-by: Arvind Yadav <[e-mail]>
Reviewed-by: Chanwoo Choi <[e-mail]>
Signed-off-by: MyungJoo Ham <[e-mail]>

drivers/devfreq/governor_userspace.c

···
 	&dev_attr_set_freq.attr,
 	NULL,
 };
-static struct attribute_group dev_attr_group = {
+static const struct attribute_group dev_attr_group = {
 	.name	= "userspace",
 	.attrs	= dev_entries,
 };