[media] gspca - sonixj: Better scanning of isochronous packets

A marker 'ff ff 00 c4 c4 96' indicates an end of frame.
It is 62 bytes long and may be splitted on 2 packets.
It contains a flag 'USB full' which indicates that the frame is truncated.

Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>