efi: x86: make kobj_type structure constant

Since commit ee6d3dd4 ("driver core: make kobj_type constant.")
the driver core allows the usage of const struct kobj_type.

Take advantage of this to constify the structure definition to prevent
modification at runtime.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/x86/platform/efi/runtime-map.c

@@ -93,7 +93,7 @@ static void map_release(struct kobject *kobj)
 	kfree(entry);
 }
 
-static struct kobj_type __refdata map_ktype = {
+static const struct kobj_type __refconst map_ktype = {
 	.sysfs_ops	= &map_attr_ops,
 	.default_groups	= def_groups,
 	.release	= map_release,