io_uring: consolidate drain seq checking

We check sequences when queuing drained requests as well when flushing
them. Instead, always queue and immediately try to flush, so that all
seq handling can be kept contained in the flushing code.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d4651f742e671af5b3216581e539ea5d31bc7125.1746788718.git.asml.silence@gmail.com


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