ALSA: line6: Abort if inconsistent usbdev is found at disconnect

It's utterly unsafe to proceed further the disconnect procedure if the
assigned usbdev is inconsistent with the expected object.  Better to
put a WARN_ON() for more cautions and abort immediately.

Tested-by: Chris Rorvick <chris@rorvick.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/line6/driver.c

@@ -585,12 +585,12 @@ void line6_disconnect(struct usb_interface *interface)
 	if (!line6)
 		return;
 
+	if (WARN_ON(usbdev != line6->usbdev))
+		return;
+
 	if (line6->urb_listen != NULL)
 		line6_stop_listen(line6);
 
-	if (usbdev != line6->usbdev)
-		dev_err(line6->ifcdev, "driver bug: inconsistent usb device\n");
-
 	snd_card_disconnect(line6->card);
 	if (line6->line6pcm)
 		line6_pcm_disconnect(line6->line6pcm);