[media] go7007: MJPEG buffer overflow

The go7007 driver has a potential buffer overflow and pointer corruption
bug which causes a crash while capturing MJPEG. The motion detection
(MODET) active_map array can be overflowed by JPEG frame data that
emulates a MODET start code. The active_map overflow overwrites the
active_buf pointer, causing a crash.

The JPEG data that emulated MODET start code was being removed from the
output, resulting in garbled JPEG frames. Therefore ignore MODET start
codes when MODET is not enabled.

Signed-off-by: Pete Eberlein <pete@sensoray.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>