Fix pluginwatcher panic on failed startup

pkg/kubelet/util/pluginwatcher/plugin_watcher.go

@@ -187,7 +187,9 @@ func (w *Watcher) traversePluginDir(dir string) error {
 				return fmt.Errorf("failed to watch %s, err: %v", path, err)
 			}
 		case mode&os.ModeSocket != 0:
+			w.wg.Add(1)
 			go func() {
+				defer w.wg.Done()
 				w.fsWatcher.Events <- fsnotify.Event{
 					Name: path,
 					Op:   fsnotify.Create,