pass the correct argument to create the JMESPath

The filed was passed to create the JMESPath when creating the groupsFieldName, however this was not a string that had been passed through `Util.fixEmptyAndTrim` which caused exceptions to be logged when not using groups

src/main/java/org/jenkinsci/plugins/oic/OicSecurityRealm.java

@@ -744,7 +744,7 @@ private Object applyJMESPath(Expression<Object> expression, Object map) {
     @DataBoundSetter
     public void setGroupsFieldName(String groupsFieldName) {
         this.groupsFieldName = Util.fixEmptyAndTrim(groupsFieldName);
-        this.groupsFieldExpr = this.compileJMESPath(groupsFieldName, "groups field");
+        this.groupsFieldExpr = this.compileJMESPath(this.groupsFieldName, "groups field");
     }
 
     @DataBoundSetter