io_uring: improve sq_thread waiting check

If SQPOLL task finds a ring requesting it to continue running, no need
to set wake flag to rest of the rings as it will be cleared in a moment
anyway, so hide it in a single sqd->ctx_list loop.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1ee5a696d9fd08645994c58ee147d149a8957d94.1621201931.git.asml.silence@gmail.com


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