oxnas: dts: Unify naming of gpio-keys nodes

In DTS Checklist[1] we're now demanding proper generic node names, as
the name of a node should reflect the function of the device and use
generic name for that[2]. Everybody seems to be copy&pasting from DTS
files available in the repository today, so let's unify that naming
there as well and provide proper examples.

1. https://openwrt.org/submitting-patches#dts_checklist
2. https://github.com/devicetree-org/devicetree-specification/blob/master/source/devicetree-basics.rst#generic-names-recommendation



Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com> [split up]

target/linux/oxnas/files/arch/arm/boot/dts/ox820-akitio-mycloud.dts

@@ -39,7 +39,7 @@
 		};
 	};
 
-	gpio-keys-polled {
+	keys {
 		compatible = "gpio-keys-polled";
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_buttons>;

target/linux/oxnas/files/arch/arm/boot/dts/ox820-mitrastar-stg212.dts

@@ -25,7 +25,7 @@
 		gpio1 = &gpio1;
 	};
 
-	gpio-keys-polled {
+	keys {
 		compatible = "gpio-keys-polled";
 		#address-cells = <1>;
 		#size-cells = <0>;

target/linux/oxnas/files/arch/arm/boot/dts/ox820-shuttle-kd20.dts

@@ -37,7 +37,7 @@
 		};
 	};
 
-	gpio-keys-polled {
+	keys {
 		compatible = "gpio-keys-polled";
 		#address-cells = <1>;
 		#size-cells = <0>;