dt-bindings: display: synopsys,dw-hdmi: drop ref from reg-io-width

reg-io-width is a standard property, so no need for defining its type
with $ref.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/display/bridge/synopsys,dw-hdmi.yaml

···
   reg-io-width:
     description:
       Width (in bytes) of the registers specified by the reg property.
-    $ref: /schemas/types.yaml#/definitions/uint32
     enum: [1, 4]
     default: 1