io_uring: fix not initialised work->flags

59960b9d ("io_uring: fix lazy work init") tried to fix missing
io_req_init_async(), but left out work.flags and hash. Do it earlier.

Fixes: 7cdaf587

 ("io_uring: avoid whole io_wq_work copy for requests completed inline")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>