dt-bindings: leds: lp50xx: correct reg/unit addresses in example

The multi-led node defined address/size cells, so it is intended to have
children with unit addresses.

The second multi-led's reg property defined three LED indexes within one
reg item, which is not correct - these are three separate items.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220607075247.58048-1-krzysztof.kozlowski@linaro.org