Fix issue reported by error-prone

Change-Id: Ide991f2b91fbd4d7652da6ff8e5a1868dd62dc22
diff --git a/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/McastHandler.java b/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/McastHandler.java
index ce2c2da..94b3a4c 100644
--- a/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/McastHandler.java
+++ b/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/McastHandler.java
@@ -523,7 +523,7 @@
                 return;
             }
             // Let's add the port and reuse the previous one
-            portBuilder.addAll(existingPorts).add(port).build();
+            portBuilder.addAll(existingPorts).add(port);
             // Reuse previous nextObj
             newNextObj = nextObjBuilder(mcastIp, assignedVlan,
                                         portBuilder.build(), nextObj.id()).addToExisting();