ipq40xx: re-add label MAC address for FritzBox 4040

The MAC address of the GMAC is contained inside the CWMP-Account
number on the label.

The label MAC address alias was defined previously, but it has been
removed with the switch to IPQESS / DSA.

Restore the label MAC address alias.

Fixes: 27b441c ("ipq40xx: drop ESSEDMA + AR40xx DTS nodes")
Signed-off-by: Fabian Bläse <fabian@blaese.de>

target/linux/ipq40xx/files/arch/arm/boot/dts/qcom-ipq4018-fritzbox-4040.dts

@@ -14,6 +14,7 @@
 		led-failsafe = &flash;
 		led-running = &power;
 		led-upgrade = &flash;
+		label-mac-device = &gmac;
 	};
 
 	soc {