ARM: dts: porter: Fix HDMI output routing

The HDMI encoder is connected to the RGB output of the DU, which is
port@0, not port@1. Fix the incorrect DT description.

Fixes: c5af8a42 ("ARM: dts: porter: add DU DT support")
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7791-porter.dts

@@ -425,7 +425,7 @@ &du {
 		      "dclkin.0", "dclkin.1";
 
 	ports {
-		port@1 {
+		port@0 {
 			endpoint {
 				remote-endpoint = <&adv7511_in>;
 			};