[media] gspca_zc3xx: Fix setting of jpeg quality while streaming

When the user changes the JPEG quality while the camera is streaming, the
driver should not only change the JPEG headers send to userspace, but also
actually tell the camera to use a different quantization table.

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