V4L/DVB (10280): cx18: Rename structure members: dev to pci_dev and v4l2dev to video_dev

Renamed structure member name to be more specific to type in anticipation
of updating to the v4l2_device/v4l2_subdev framework.  Too many objects named
"dev" and /v4l2_\{0,1\}dev/ would be to confusing.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>