io_uring: simplify reissue in kiocb_done

Simplify failed resubmission prep in kiocb_done(), it's a bit ugly with
conditional logic and hand handling cflags / select buffers. Instead,
punt to tw and use io_req_task_complete() already handling all the
cases.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/667c33484b05b612e9420e1b1d5f4dc46d0ee9ce.1637524285.git.asml.silence@gmail.com


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