V4L/DVB (10271): saa7146: convert to video_ioctl2.

The conversion to video_ioctl2 is the first phase to converting this driver
to the latest v4l2 framework.

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