[media] v4l/cx18: update workqueue usage

With cmwq, there's no reason to use separate out_work_queue.  Drop it
and use system_wq instead.  The in_work_queue needs to be ordered so
can't use one of the system wqs; however, as it isn't used to reclaim
memory, allocate the workqueue with alloc_ordered_workqueue() without
WQ_MEM_RECLAIM.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andy Walls <awalls@md.metrocast.net>
Acked-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>