mm/page_idle.c: constify attribute_group structures

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

Link: http://lkml.kernel.org/r/1501157221-3832-1-git-send-email-arvind.yadav.cs@gmail.com
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_idle.c

@@ -204,7 +204,7 @@ static struct bin_attribute *page_idle_bin_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group page_idle_attr_group = {
+static const struct attribute_group page_idle_attr_group = {
 	.bin_attrs = page_idle_bin_attrs,
 	.name = "page_idle",
 };