USB: fix transvibrator disconnect race

in disconnect you set the interface's private data to NULL. In your IO
methods you unconditionally follow the pointer into never never land.

Signed-off-by: Oliver Neukum <oliver@neukum.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/misc/trancevibrator.c

@@ -120,8 +120,8 @@ static void tv_disconnect(struct usb_interface *interface)
 	struct trancevibrator *dev;
 
 	dev = usb_get_intfdata (interface);
-	usb_set_intfdata(interface, NULL);
 	device_remove_file(&interface->dev, &dev_attr_speed);
+	usb_set_intfdata(interface, NULL);
 	usb_put_dev(dev->udev);
 	kfree(dev);
 }