[media] gspca: Don't use video_device_node_name in v4l2_device release handler

When the v4l2_device release handler gets called the kobject under
vdev->dev has already been released, so we cannot use kobject_name on
it (which video_device_node_name does).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>