[media] adv7604: Set HPD GPIO direction to output

The HPD GPIO is used as an output but its direction is never set. Fix
it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>