Fix Javadoc warnings

Change-Id: Icf8b6b6f77ea80d3975aa975226a178145067adf
diff --git a/apps/optical-model/src/main/java/org/onosproject/net/optical/device/OmsPortHelper.java b/apps/optical-model/src/main/java/org/onosproject/net/optical/device/OmsPortHelper.java
index f0d878d..2d83aa2 100644
--- a/apps/optical-model/src/main/java/org/onosproject/net/optical/device/OmsPortHelper.java
+++ b/apps/optical-model/src/main/java/org/onosproject/net/optical/device/OmsPortHelper.java
@@ -66,6 +66,7 @@
      * @param maxFrequency  maximum frequency
      * @param grid          grid spacing frequency
      * @param annotations   key/value annotations map
+     * @return              port description
      */
     public static PortDescription omsPortDescription(PortNumber number,
                                               boolean isEnabled,
@@ -93,6 +94,7 @@
      * @param minFrequency  minimum frequency
      * @param maxFrequency  maximum frequency
      * @param grid          grid spacing frequency
+     * @return              port description
      */
     public static PortDescription omsPortDescription(PortNumber number,
                                               boolean isEnabled,
@@ -110,6 +112,7 @@
      * @param maxFrequency  maximum frequency
      * @param grid          grid spacing frequency
      * @param annotations   key/value annotations map
+     * @return              port description
      */
     public static PortDescription omsPortDescription(PortDescription base,
                                               Frequency minFrequency,