port-mbim: add missing guard for try_qmi_over_mbim in mm_port_mbim_open()

Fixes: c0cc694c67

src/mm-port-mbim.c

@@ -335,9 +335,11 @@ mm_port_mbim_open (MMPortMbim          *self,
     fullpath = g_strdup_printf ("/dev/%s", mm_port_get_device (MM_PORT (self)));
     file = g_file_new_for_path (fullpath);
 
+#if WITH_QMI && QMI_MBIM_QMUX_SUPPORTED
     /* If we want to try QMI over MBIM, store the GFile as task data */
     if (try_qmi_over_mbim)
         g_task_set_task_data (task, g_object_ref (file), g_object_unref);
+#endif
 
     self->priv->in_progress = TRUE;
     mbim_device_new (file,