io_uring: fix io_match_task must_hold

The __must_hold annotation in io_match_task() uses a non existing
parameter "req", fix it.

Fixes: 6af3f48b ("io_uring: fix link traversal locking")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/3e65ee7709e96507cef3d93291746f2c489f2307.1721819383.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/timeout.c

@@ -639,7 +639,7 @@ void io_queue_linked_timeout(struct io_kiocb *req)
 
 static bool io_match_task(struct io_kiocb *head, struct task_struct *task,
 			  bool cancel_all)
-	__must_hold(&req->ctx->timeout_lock)
+	__must_hold(&head->ctx->timeout_lock)
 {
 	struct io_kiocb *req;