firmware/efi: 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.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-14-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

drivers/firmware/efi/efi.c

@@ -179,7 +179,7 @@ static umode_t efi_attr_is_visible(struct kobject *kobj,
 	return attr->mode;
 }
 
-static struct attribute_group efi_subsys_attr_group = {
+static const struct attribute_group efi_subsys_attr_group = {
 	.attrs = efi_subsys_attrs,
 	.is_visible = efi_attr_is_visible,
 };