V4L/DVB: ivtv: move the _IO() decoder ioctls into vidioc_default

Now that video_ioctl2 no longer clobbers the argument for _IO() ioctls we
can move these into vidioc_default where they really belong.

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