ARM: dts: exynos: fix PWM LED max brightness on Odroid XU/XU3

There is no "max_brightness" property.  This brings the intentional
brightness reduce of green LED and dtschema checks as well:

  arch/arm/boot/dts/exynos5410-odroidxu.dt.yaml: led-controller-1: led-1: 'max-brightness' is a required property

Fixes: 719f39fe ("ARM: dts: exynos5422-odroidxu3: Hook up PWM and use it for LEDs")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210505135941.59898-3-krzysztof.kozlowski@canonical.com

arch/arm/boot/dts/exynos54xx-odroidxu-leds.dtsi

@@ -22,7 +22,7 @@ led-1 {
 			 * Green LED is much brighter than the others
 			 * so limit its max brightness
 			 */
-			max_brightness = <127>;
+			max-brightness = <127>;
 			linux,default-trigger = "mmc0";
 		};
 
@@ -30,7 +30,7 @@ led-2 {
 			label = "blue:heartbeat";
 			pwms = <&pwm 2 2000000 0>;
 			pwm-names = "pwm2";
-			max_brightness = <255>;
+			max-brightness = <255>;
 			linux,default-trigger = "heartbeat";
 		};
 	};