[media] gspca-pac207: Add a led_invert module parameter

Some cams have their led connected in such a way that on = off and visa versa
unfortunately we cannot tell this from the driver in any way, so add a module
parameter for this.

Reported-by: Yuri Glushkov <yglushkov@yahoo.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>