io_uring: correct io_queue_async_work() traces

Request's io-wq work is hashed in io_prep_async_link(), so
as trace_io_uring_queue_async_work() looks at it should follow after
prep has been done.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/709c9f872f4d2e198c7aed9c49019ca7095dd24d.1616366969.git.asml.silence@gmail.com


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