ARM: dts: rockchip: add label property for leds on Radxa Rock

The leds-gpio driver recently switched to the device property API. The device_node
name is no longer retrieved if the "label" devicetree property is not found.
In this case the driver tries to create entries with (null) name in
/sys/class/leds, which is wrong and generates backtrace as several gpio_leds have
the same name. Also renamed subnode "yellow" to "blue" to match the last
schematics updates.
Signed-off-by: Romain Perier <romain.perier@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3188-radxarock.dts

@@ -43,16 +43,19 @@ gpio-leds {
 		compatible = "gpio-leds";
 
 		green {
+			label = "rock:green:user1";
 			gpios = <&gpio0 12 GPIO_ACTIVE_LOW>;
 			default-state = "off";
 		};
 
-		yellow {
+		blue {
+			label = "rock:blue:user2";
 			gpios = <&gpio0 14 GPIO_ACTIVE_LOW>;
 			default-state = "off";
 		};
 
 		sleep {
+			label = "rock:red:power";
 			gpios = <&gpio0 15 0>;
 			default-state = "off";
 		};