Fix Sonar issue:

Strings literals should be placed on the left side when checking for
equality

Change-Id: I4537e08936731ace55aeecb3ad941269ec1eb191
diff --git a/apps/optical/src/main/java/org/onosproject/optical/OpticalLinkProvider.java b/apps/optical/src/main/java/org/onosproject/optical/OpticalLinkProvider.java
index b198027..1e32592 100644
--- a/apps/optical/src/main/java/org/onosproject/optical/OpticalLinkProvider.java
+++ b/apps/optical/src/main/java/org/onosproject/optical/OpticalLinkProvider.java
@@ -110,7 +110,7 @@
         public void event(LinkEvent event) {
             if (event.type() == LinkEvent.Type.LINK_ADDED) {
                 Link link = event.subject();
-                if (link.providerId().scheme().equals("cfg")) {
+                if ("cfg".equals(link.providerId().scheme())) {
                     processLink(event.subject());
                 }
             }