dt-bindings: net: dsa: mediatek,mt7530: Add missing 'reg' property

The 'reg' property is missing from the mediatek,mt7530 schema which
results in the following warning once 'unevaluatedProperties' is fixed:

Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.example.dtb: switch@0: Unevaluated properties are not allowed ('reg' was unexpected)

Fixes: e0dda311 ("dt-bindings: net: dsa: convert binding for mediatek switches")
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20220701222240.1706272-1-robh@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml

@@ -66,6 +66,9 @@ properties:
       - mediatek,mt7531
       - mediatek,mt7621
 
+  reg:
+    maxItems: 1
+
   core-supply:
     description:
       Phandle to the regulator node necessary for the core power.