Correct misspelled OVS plugin variable

Fixes bug 1071567, the broken setup of external gateway IP/routes
when using quantum with the openvswitch plugin due to a misspelled
variable name.

Change-Id: I950701a55f770cf075bca500e5a935628f6bf14a
diff --git a/lib/quantum b/lib/quantum
index 0b26622..f9e1782 100644
--- a/lib/quantum
+++ b/lib/quantum
@@ -50,7 +50,7 @@
 }
 
 function is_quantum_ovs_base_plugin() {
-    local plguin=$1
+    local plugin=$1
     if [[ ",openvswitch,ryu," =~ ,${plugin}, ]]; then
         return 0
     fi