ARM: dts: imx28-apf28dev: fix user button polarity

Signed-off-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@armadeus.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx28-apf28dev.dts

@@ -223,7 +223,7 @@
 
 		user-button {
 			label = "User button";
-			gpios = <&gpio0 17 0>;
+			gpios = <&gpio0 17 GPIO_ACTIVE_LOW>;
 			linux,code = <0x100>;
 		};
 	};