ARM: dts: sun7i: Remove gpio-keys warnings

Some gpio-keys definitions in our DTs were having buttons defined with a
unit-address and that would generate a DTC warning.

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

arch/arm/boot/dts/sun7i-a20-pcduino3.dts

@@ -75,21 +75,22 @@ rx {
 		};
 	};
 
-	gpio_keys {
+	gpio-keys {
 		compatible = "gpio-keys";
-		#address-cells = <1>;
-		#size-cells = <0>;
-		button@0 {
+
+		back {
 			label = "Key Back";
 			linux,code = <KEY_BACK>;
 			gpios = <&pio 7 17 GPIO_ACTIVE_LOW>;
 		};
-		button@1 {
+
+		home {
 			label = "Key Home";
 			linux,code = <KEY_HOME>;
 			gpios = <&pio 7 18 GPIO_ACTIVE_LOW>;
 		};
-		button@2 {
+
+		menu {
 			label = "Key Menu";
 			linux,code = <KEY_MENU>;
 			gpios = <&pio 7 19 GPIO_ACTIVE_LOW>;