v4l: vsp1: Don't set WPF sink pointer

The sink pointer is used to configure routing inside the VSP, and as
such must point to the next VSP entity in the pipeline. The WPF being a
pipeline terminal sink, its output route can't be configured. The
routing configuration code already handles this correctly without
referring to the sink pointer, which thus doesn't need to be set.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Acked-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>