ARM: dts: mmp2-olpc-xo-1-75: Use plural form of "-gpios"

This makes validation happier.

Link: https://lore.kernel.org/r/20200925234805.228251-3-lkundrak@v3.skSigned-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/boot/dts/mmp2-olpc-xo-1-75.dts

@@ -227,12 +227,12 @@ &ssp3 {
 	/delete-property/ #size-cells;
 	spi-slave;
 	status = "okay";
-	ready-gpio = <&gpio 125 GPIO_ACTIVE_HIGH>;
+	ready-gpios = <&gpio 125 GPIO_ACTIVE_HIGH>;
 
 	slave {
 		compatible = "olpc,xo1.75-ec";
 		spi-cpha;
-		cmd-gpio = <&gpio 155 GPIO_ACTIVE_HIGH>;
+		cmd-gpios = <&gpio 155 GPIO_ACTIVE_HIGH>;
 	};
 };