io_uring: signal SQPOLL task_work with TWA_SIGNAL_NO_IPI

Before SQPOLL was transitioned to managing its own task_work, the core
used TWA_SIGNAL_NO_IPI to ensure that task_work was processed. If not,
we can't be sure that all task_work is processed at SQPOLL thread exit
time.

Fixes: af5d68f8

 ("io_uring/sqpoll: manage task_work privately")
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>