V4L/DVB (9552): gspca: Simplify the ISOC packet scanning in tv8532.

This patch
- makes unuseful the temporary buffers
- and also fixes the bad colors problem.

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