ARM: dts: dove: fix PCA95xx GPIO expander properties on A510

The PCA95xx GPIO expander requires GPIO controller properties to operate
properly.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Gregory CLEMENT <[e-mail]>

arch/arm/boot/dts/dove-sbc-a510.dts

···
 	gpio_ext: gpio@20 {
 		compatible = "nxp,pca9555";
 		reg = <0x20>;
+		gpio-controller;
 		#gpio-cells = <2>;
 	};
 };