ARM: dts: stm32: Fix schema warnings for pwm-leds on lxa-mc1

The node names for devices using the pwm-leds driver follow a certain
naming scheme (now).  Parent node name is not enforced, but recommended
by DT project.

  DTC     arch/arm/boot/dts/stm32mp157c-lxa-mc1.dt.yaml
  CHECK   arch/arm/boot/dts/stm32mp157c-lxa-mc1.dt.yaml
/home/alex/build/linux/arch/arm/boot/dts/stm32mp157c-lxa-mc1.dt.yaml: led-rgb: 'led-blue', 'led-green', 'led-red' do not match any of the regexes: '^led(-[0-9a-f]+)?$', 'pinctrl-[0-9]+'
        From schema: /home/alex/src/linux/leds/Documentation/devicetree/bindings/leds/leds-pwm.yaml
Signed-off-by: Alexander Dahl <post@lespocky.de>
Acked-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32mp157c-lxa-mc1.dts

@@ -36,34 +36,35 @@ chosen {
 		stdout-path = &uart4;
 	};
 
-	led-act {
+	led-controller-0 {
 		compatible = "gpio-leds";
 
-		led-green {
+		led-0 {
 			label = "mc1:green:act";
 			gpios = <&gpioa 13 GPIO_ACTIVE_LOW>;
 			linux,default-trigger = "heartbeat";
 		};
 	};
 
-	led-rgb {
+	led-controller-1 {
 		compatible = "pwm-leds";
 
-		led-red {
+		/* led-1 to led-3 are part of a single RGB led */
+		led-1 {
 			label = "mc1:red:rgb";
 			pwms = <&leds_pwm 1 1000000 0>;
 			max-brightness = <255>;
 			active-low;
 		};
 
-		led-green {
+		led-2 {
 			label = "mc1:green:rgb";
 			pwms = <&leds_pwm 2 1000000 0>;
 			max-brightness = <255>;
 			active-low;
 		};
 
-		led-blue {
+		led-3 {
 			label = "mc1:blue:rgb";
 			pwms = <&leds_pwm 3 1000000 0>;
 			max-brightness = <255>;