[media] gspca_pac7302: make red balance and blue balance controls work again

Fix a regression from kernel 3.4 which has been introduced with the conversion of the gspca driver to the v4l2 control framework.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Cc: stable@kernel.org
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>