V4L/DVB (8377): ivtv/cx18: ensure the default control values are correct

For several MPEG controls and the volume control the default as returned
by VIDIOC_QUERYCTRL was incorrect and did not match the actual initial
value.

This is now fixed for cx18 and ivtv.

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