V4L/DVB (10625): ivtv: fix decoder crash regression

The video_ioctl2 conversion of ivtv in kernel 2.6.27 introduced a bug
causing decoder commands to crash. The decoder commands should have been
handled from the video_ioctl2 default handler, ensuring correct mapping
of the argument between user and kernel space. Unfortunately they ended
up before the video_ioctl2 call, causing random crashes.

Thanks to hannes@linus.priv.at for testing and helping me track down the
cause!

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