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.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>