arm64: dts: armada-3720: align LED node name with bindings

Bindings expect the LED node names to follow certain pattern, see
dtbs_check warnings:

  armada-3720-gl-mv1000.dtb: leds: 'power', 'vpn', 'wan' do not match any of the regexes: '(^led-[0-9a-f]$|led)', 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>

arch/arm64/boot/dts/marvell/armada-3720-gl-mv1000.dts

@@ -57,17 +57,17 @@ switch {
 	leds {
 		compatible = "gpio-leds";
 
-		vpn {
+		led-vpn {
 			label = "green:vpn";
 			gpios = <&gpionb 11 GPIO_ACTIVE_LOW>;
 		};
 
-		wan {
+		led-wan {
 			label = "green:wan";
 			gpios = <&gpionb 12 GPIO_ACTIVE_LOW>;
 		};
 
-		led_power: power {
+		led_power: led-power {
 			label = "green:power";
 			gpios = <&gpionb 13 GPIO_ACTIVE_LOW>;
 			default-state = "on";