V4L/DVB (7337): ivtv: fix polling bug

The q_io queue was never taken into account by the poll function. Thanks to
Andy Walls for finding this bug.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>