lantiq/xrx200: fix WLAN button actions for Fritzbox 3370

The WLAN button actions are reversed, i.e. pressing the button emits a
'released' action, and vice versa.
This can easily be checked by adding
logger -t button_action "$BUTTON $ACTION"
as the second line of /etc/rc.button/rfkill, and using logread to read
the events (assuming the preceding patch has been applied).
Defining the GPIO as ACTIVE_LOW corrects this behavior.

Signed-off-by: Dustin Gathmann <dzsoftware@posteo.org>
(cherry picked from commit 0ee30adb46)

target/linux/lantiq/files-4.14/arch/mips/boot/dts/FRITZ3370-REV2.dtsi

@@ -45,7 +45,7 @@
 
 		wifi {
 			label = "wlan";
-			gpios = <&gpio 29 GPIO_ACTIVE_HIGH>;
+			gpios = <&gpio 29 GPIO_ACTIVE_LOW>;
 			linux,code = <KEY_RFKILL>;
 		};
 	};