io_uring: refactor __io_cq_unlock_post_flush()

Separate ->task_complete path in __io_cq_unlock_post_flush().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/baa9b8d822f024e4ee01c40209dbbe38d9c8c11d.1680782017.git.asml.silence@gmail.com


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