port-qmi: Increase the reference counter of the QrtrNode

Currently, we are not increasing the reference counter of the QrtrNode
when creating a PortQmi for a QRTR port, and we are clearing the object
when disposing the port.

src/mm-port-qmi.c

@@ -2525,8 +2525,8 @@ set_property (GObject      *object,
 
     switch (prop_id) {
     case PROP_NODE:
-        /* construct only, no new reference! */
-        self->priv->node = g_value_get_object (value);
+        g_clear_object (&self->priv->node);
+        self->priv->node = g_value_dup_object (value);
         break;
     default:
         G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);