dt-bindings: media: adv7180: Add missing video-interfaces.yaml reference

The adv7180 binding is using 'bus-width' property, but doesn't document it.
Add a reference to the video-interfaces.yaml schema to properly document it.

Fixes: 066a94e2 ("media: dt-bindings: media: Use graph and video-interfaces schemas")
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210623164256.2569839-1-robh@kernel.org

Documentation/devicetree/bindings/media/i2c/adv7180.yaml

@@ -36,7 +36,13 @@ properties:
     maxItems: 1
 
   port:
-    $ref: /schemas/graph.yaml#/properties/port
+    $ref: /schemas/graph.yaml#/$defs/port-base
+    unevaluatedProperties: false
+
+    properties:
+      endpoint:
+        $ref: /schemas/media/video-interfaces.yaml#
+        unevaluatedProperties: false
 
   ports: true