dt-bindings: iio: rohm,bu27010: add missing vdd-supply to example

Bindings require vdd-supply but the example DTS was missing one.  This
fixes dt_binding_check error:

  Documentation/devicetree/bindings/iio/light/rohm,bu27010.example.dtb: light-sensor@38: 'vdd-supply' is a required property

Fixes: ce2a8c16

 ("dt-bindings: iio: ROHM BU27010 RGBC + flickering sensor")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/20230808063223.80431-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>