[media] v4l: vsp1: Remove struct vsp1_pipeline num_video field

The field is always equal to the num_inputs field plus one, remove the
duplicate.

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