Fixed NPE in ServiceBundle introduced by a recent merge.

Change-Id: I24655f086e4142b359a53a443c8d4b58c93fa525
diff --git a/web/gui/src/main/java/org/onosproject/ui/impl/topo/util/ServicesBundle.java b/web/gui/src/main/java/org/onosproject/ui/impl/topo/util/ServicesBundle.java
index 76c72f3..3ae7e90 100644
--- a/web/gui/src/main/java/org/onosproject/ui/impl/topo/util/ServicesBundle.java
+++ b/web/gui/src/main/java/org/onosproject/ui/impl/topo/util/ServicesBundle.java
@@ -67,6 +67,7 @@
 
         topologyService = directory.get(TopologyService.class);
         deviceService = directory.get(DeviceService.class);
+        driverService = directory.get(DriverService.class);
         hostService = directory.get(HostService.class);
         linkService = directory.get(LinkService.class);
         tunnelService = directory.get(TunnelService.class);