staging: frontier: use after free in disconnect()

usb_alphatrack_delete() frees "dev" so we can't use it on that path.

Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/frontier/alphatrack.c

···
 		mutex_unlock(&dev->mtx);
 		usb_alphatrack_delete(dev);
 	} else {
+		atomic_set(&dev->writes_pending, 0);
 		dev->intf = NULL;
 		mutex_unlock(&dev->mtx);
 	}
 
-	atomic_set(&dev->writes_pending, 0);
 	mutex_unlock(&disconnect_mutex);
 
 	dev_info(&intf->dev, "Alphatrack Surface #%d now disconnected\n",