ARM: dts: sunxi: Change LRADC node names to avoid warnings

One of the usage of the LRADC is to implement buttons. The bindings define
that we should have one subnode per button, with their associated voltage
as a property.

However, there was no reg property but we still used the voltage associated
to the button as the unit-address, which eventually generated warnings in
DTC.

Rename the node names to avoid those warnings.
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>

arch/arm/boot/dts/sunxi-reference-design-tablet.dtsi

@@ -60,14 +60,14 @@ &lradc {
 	vref-supply = <&reg_vcc3v0>;
 	status = "okay";
 
-	button@200 {
+	button-200 {
 		label = "Volume Up";
 		linux,code = <KEY_VOLUMEUP>;
 		channel = <0>;
 		voltage = <200000>;
 	};
 
-	button@400 {
+	button-400 {
 		label = "Volume Down";
 		linux,code = <KEY_VOLUMEDOWN>;
 		channel = <0>;