io_uring: refactor __io_req_complete_post

Keep parts of __io_req_complete_post() relying on req->flags together so
the value can be cached.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2b4fbb42f404a0e75c4d9f0a5b16f314a839d0a9.1673887636.git.asml.silence@gmail.com


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