V4L/DVB (9800): cx18: Eliminate q_io from stream buffer handling

Eliminate q_io from stream buffer handling in anticipation of upcoming
changes in buffer handling.  q_io was a holdover from ivtv and it's function
in cx18 was trivial and not necessary.  We just push things back onto the
front of q_full now, instead of maintaining a 1 buffer q_io queue.

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