ath79: add label MAC address for Ubiquiti Picostation M (XM)

This adds the label MAC address for the Ubiquiti Picostation M (XM).
This was overlooked when adding support in the previous patch.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ath79/generic/base-files/etc/board.d/02_network

@@ -430,6 +430,7 @@ ath79_setup_macs()
 	ubnt,bullet-m|\
 	ubnt,nanostation-loco-m|\
 	ubnt,nanostation-m|\
+	ubnt,picostation-m|\
 	ubnt,rocket-m|\
 	ubnt,unifi)
 		label_mac=$(cat /sys/class/ieee80211/phy0/macaddress)