V4L/DVB (9873): gspca - ov534: Improve payload handling.

Frame data in bulk transfers is separated into 2048-byte payloads.
Each payload has its own header.

Signed-off-by: Jim Paris <jim@jtan.com>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>