zcip.script: fix $ip environment variable

The environment variable containing the IP address allocated by zcip
is "ip" and not "IP".

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/examples/zcip.script b/examples/zcip.script
index 988e542..e543c30 100755
--- a/examples/zcip.script
+++ b/examples/zcip.script
@@ -20,9 +20,9 @@
 		exit 1
 	fi
 	# remember $ip for $interface, to use on restart
-	if [ "x$IP" != x -a -w "$IP.$interface" ]
+	if [ "x$ip" != x -a -w "$ip.$interface" ]
 	then
-		echo $ip > "$IP.$interface"
+		echo $ip > "$ip.$interface"
 	fi
 	exec ip address add dev $interface \
 		scope link local "$ip/16" broadcast +