OS-2910 sdev_node_t can end up associated with wrong sdev_plugin_t

@@ -960,10 +960,11 @@
 
         /* return node to initial state as per constructor */
         (void) memset((void *)&dv->sdev_instance_data, 0,
             sizeof (dv->sdev_instance_data));
         vn_invalid(SDEVTOV(dv));
+        dv->sdev_private = NULL;
         kmem_cache_free(sdev_node_cache, dv);
 }
 
 /*
  * DIRECTORY CACHE lookup