ramips: fix network setup for Ubiquiti ER-X/ER-X-SFP

The function name ucidef_set_interface_lan_wan does not exist,
use the proper name by adding an "s" and thereby fix network
setup on these devices.

Fixes: 22468cc40c (ramips: erx and erx-sfp: fix missing WAN interface)

Signed-off-by: Nelson Cai <niphor@gmail.com>
[commit message/title facelift]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ramips/mt7621/base-files/etc/board.d/02_network

@@ -48,10 +48,10 @@ ramips_setup_interfaces()
 		ucidef_set_interfaces_lan_wan "lan2 lan3 lan4 lan5" "wan"
 		;;
 	ubnt,edgerouter-x)
-		ucidef_set_interface_lan_wan "eth1 eth2 eth3 eth4" "eth0"
+		ucidef_set_interfaces_lan_wan "eth1 eth2 eth3 eth4" "eth0"
 		;;
 	ubnt,edgerouter-x-sfp)
-		ucidef_set_interface_lan_wan "eth1 eth2 eth3 eth4 eth5" "eth0"
+		ucidef_set_interfaces_lan_wan "eth1 eth2 eth3 eth4 eth5" "eth0"
 		;;
 	zyxel,wap6805)
 		ucidef_set_interface_lan "lan1 lan2 lan3 lan4"