aio: avoid pointless cred reference count bump

iocb->fsync.creds already holds a reference count that is stable while
the operation is performed.

Link: https://lore.kernel.org/r/20241125-work-cred-v2-10-68b9d38bb5b2@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

fs/aio.c

@@ -1639,10 +1639,10 @@ static int aio_write(struct kiocb *req, const struct iocb *iocb,
 static void aio_fsync_work(struct work_struct *work)
 {
 	struct aio_kiocb *iocb = container_of(work, struct aio_kiocb, fsync.work);
-	const struct cred *old_cred = override_creds(get_new_cred(iocb->fsync.creds));
+	const struct cred *old_cred = override_creds(iocb->fsync.creds);
 
 	iocb->ki_res.res = vfs_fsync(iocb->fsync.file, iocb->fsync.datasync);
-	put_cred(revert_creds(old_cred));
+	revert_creds(old_cred);
 	put_cred(iocb->fsync.creds);
 	iocb_put(iocb);
 }