dt-bindings: display/msm: hdmi: Fix constraints on additional 'port' properties

The MSM HDMI port nodes are missing any restrictions on additional
properties. The $ref should be to "/properties/port" rather than
"/$defs/port-base" as there are not additional properties in the nodes
to define.

Signed-off-by: Rob Herring (Arm) <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/652299/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

Documentation/devicetree/bindings/display/msm/hdmi.yaml

···
     $ref: /schemas/graph.yaml#/properties/ports
     properties:
       port@0:
-        $ref: /schemas/graph.yaml#/$defs/port-base
+        $ref: /schemas/graph.yaml#/properties/port
         description: |
           Input endpoints of the controller.
 
       port@1:
-        $ref: /schemas/graph.yaml#/$defs/port-base
+        $ref: /schemas/graph.yaml#/properties/port
         description: |
           Output endpoints of the controller.