No longer assume pad number 0 is the source pad of the external entity. Find
the source pad from the external entity and use it instead.
Signed-off-by: NSakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>