V4L/DVB (13996): gspca_stv0680: Fix streaming on vga cameras

Streaming of VGA stv0680 based cams (instead of CIF ones) failed, because
we were using the wrong control pipe for certain commands, this patch fixes
this.

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