dt-bindings: bcm2711-hdmi: Fix broken schema

For some reason, unevaluatedProperties doesn't work and
additionalProperties is required. Fix it by switching to
additionalProperties.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210218152837.1080819-1-maxime@cerno.techSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/brcm,bcm2711-hdmi.yaml

@@ -109,7 +109,7 @@ required:
   - resets
   - ddc
 
-unevaluatedProperties: false
+additionalProperties: false
 
 examples:
   - |