dt-bindings: leds: mt6370: Fix MT6370 LED indicator DT warning

Add '$ref' and 'unevaluatedProperties: false' in 'multi-led', and remove
unused 'allOf' property.

Fixes: 440c57da ("dt-bindings: leds: mt6370: Add MediaTek MT6370 current sink type LED indicator")
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/435f6888ebc20c5abae63eb9cb3a055b60db2ed1.1665050503.git.chiaen_wu@richtek.com


Signed-off-by: Rob Herring <robh@kernel.org>