[media] sn9c102_core: add v4l2_device and replace parent with v4l2_dev

This driver did not yet support struct v4l2_device, so add it. This
make it possible to replace the deprecated parent field with the
v4l2_dev field, allowing the eventual removal of the parent field.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>