[media] gspca: Fix querycap and incorrect return codes

Add V4L2_CAP_DEVICE_CAPS support to querycap and replace -EINVAL by
-ENOTTY whenever an ioctl is not supported.

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