efivars: Use to_efivar_entry

Use to_efivar_entry() instead of open-coding it.
Signed-off-by: NGeliang Tang <geliangtang@163.com>
Signed-off-by: NMatt Fleming <matt@codeblueprint.co.uk>
Link: http://lkml.kernel.org/r/1454364428-494-9-git-send-email-matt@codeblueprint.co.ukSigned-off-by: NIngo Molnar <mingo@kernel.org>

drivers/firmware/efi/efivars.c

@@ -386,7 +386,7 @@ static const struct sysfs_ops efivar_attr_ops = {
 
 static void efivar_release(struct kobject *kobj)
 {
-	struct efivar_entry *var = container_of(kobj, struct efivar_entry, kobj);
+	struct efivar_entry *var = to_efivar_entry(kobj);
 	kfree(var);
 }