[media] v4l2-pci-skeleton.c: fill in device_caps in video_device

With the new core support for the caps the driver no longer needs
to set device_caps and capabilities in the querycap call.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>