V4L/DVB (9592): cx18: Use default kernel work queue; fix streaming flag for work handler

cx18: Use default kernel work queue; fix streaming flag for work handler.
Eliminate cx18 specific work queue and use the kernel default work queue.
Fixed the F_STREAMING_FLAG for the TS stream so cx18_dvb_work_handler()
can know when it is not safe to send MDLs to the firmware.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>