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.org


Signed-off-by: Mark Brown <broonie@kernel.org>