ublk_drv: check ubq_daemon_is_dying() in __ublk_rq_task_work()

Replace direct check on PF_EXITING in __ublk_rq_task_work() by the
existing wrapper. Also inline ubq_daemon_is_dying().

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220815023633.259825-2-ZiyangZhang@linux.alibaba.com


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