dt-bindings: power: supply: maxim,max17042: allow power-supplies

MAX17042 Fuel Gauge uses power-supplies supplies:

  arch/arm64/boot/dts/freescale/imx8mq-librem5-r2.dtb: fuel-gauge@36: 'power-supplies' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>