V4L/DVB (8552): gspca: Bad pixel format in the spca508 subdriver.

The pixel format should have been changed in changeset 6de914aaad86.

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