lantiq: tdw90x0: Fix WLAN LED on TP-Link W8970 v1.2 (FS#2232)

This patch fixes disfunctional WLAN LED on TP-Link W8970. The LED was
reported working in the CC release[1], but doesn't work anymore in 18.06.2.

1. 420cb24d41

Tested-by: Damian Janarek <dzanar18@o2.pl>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

target/linux/lantiq/files-4.14/arch/mips/boot/dts/TDW89X0.dtsi

@@ -85,6 +85,7 @@
 		wifi: wifi {
 			label = "tdw89x0:green:wifi";
 			gpios = <&ath9k 0 GPIO_ACTIVE_HIGH>;
+			linux,default-trigger = "phy0tpt";
 		};
 	};