io_uring: inline __io_req_complete_post()

There is only one user of __io_req_complete_post(), inline it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/ef4c9059950a3da5cf68df00f977f1fd13bd9306.1668597569.git.asml.silence@gmail.com


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