[media] dvbdev: use adapter arg for dvb_create_media_graph()

Instead of using media_dev argument for dvb_create_media_graph(),
use the adapter.

That allows to create a stub for this function, if compiled
without DVB support, avoiding to add extra if's at the drivers.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>