[media] v4l: vsp1: RPF entities can't be target nodes

The RPF entities are located at the very beginning of pipelines, they
can't be target nodes in the Data Path Router matrix. Remove their input
ID from the routing table.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>