Fix some unchecked conversion warnings

Change-Id: I5cfb0fceb6ab1d200fb1d7e9849ce458a2aa8ac7
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/device/impl/InternalPortEventSerializer.java b/core/store/dist/src/main/java/org/onlab/onos/store/device/impl/InternalPortEventSerializer.java
index 4f4a9e6..2facb7e 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/device/impl/InternalPortEventSerializer.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/device/impl/InternalPortEventSerializer.java
@@ -37,6 +37,8 @@
                                Class<InternalPortEvent> type) {
         ProviderId providerId = (ProviderId) kryo.readClassAndObject(input);
         DeviceId deviceId = (DeviceId) kryo.readClassAndObject(input);
+
+        @SuppressWarnings("unchecked")
         Timestamped<List<PortDescription>> portDescriptions
             = (Timestamped<List<PortDescription>>) kryo.readClassAndObject(input);