cred: return old creds from revert_creds_light()

So we can easily convert revert_creds() callers over to drop the
reference count explicitly.

Link: https://lore.kernel.org/r/20241125-work-cred-v2-2-68b9d38bb5b2@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

include/linux/cred.h

@@ -185,9 +185,12 @@ static inline const struct cred *override_creds_light(const struct cred *overrid
 	return old;
 }
 
-static inline void revert_creds_light(const struct cred *revert_cred)
+static inline const struct cred *revert_creds_light(const struct cred *revert_cred)
 {
+	const struct cred *override_cred = current->cred;
+
 	rcu_assign_pointer(current->cred, revert_cred);
+	return override_cred;
 }
 
 /**