ath79: define 2.4GHz radio for litebeam ac gen2

The litebeam ac gen2 has a 2.4GHz management radio.

Signed-off-by: Nick Hainke <[email protected]>

target/linux/ath79/dts/ar9342_ubnt_litebeam-ac-gen2.dts

@@ -33,3 +33,9 @@
 		rxdv-delay = <3>;
 	};
 };
+
+&wmac {
+	status = "okay";
+
+	mtd-cal-data = <&art 0x1000>;
+};