spi: dt-bindings: snps,dw-apb-ssi: drop ref from reg-io-width

reg-io-width is a standard property, so no need for defining its type
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220823100937.386880-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.yaml

@@ -104,7 +104,6 @@ properties:
     const: spi
 
   reg-io-width:
-    $ref: /schemas/types.yaml#/definitions/uint32
     description: I/O register width (in bytes) implemented by this device
     default: 4
     enum: [ 2, 4 ]