ARM: dts: exynos: fix PWM LED max brightness on Odroid HC1

There is no "max_brightness" property as pointed out by dtschema:

  arch/arm/boot/dts/exynos5422-odroidhc1.dt.yaml: led-controller: led-1: 'max-brightness' is a required property

Fixes: 1ac49427 ("ARM: dts: exynos: Add support for Hardkernel's Odroid HC1 board")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210505135941.59898-4-krzysztof.kozlowski@canonical.com