[media] em28xx: add support for Terratec Grabby Record led

Terratec Grabby (hw rev 2) Record led is connected to GPIO 3
and its logic is inverted: (PIO3 = 0: on, PIO3 = 1: off).

Signed-off-by: Matthieu Rogez <matthieu.rogez@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>