ALSA: line6: Don't forget to call driver's destructor at error path

Currently disconnect callback is used as a driver's destructor, and
this has to be called not only at the disconnection time but also at
the error paths during probe.
Tested-by: NChris Rorvick <chris@rorvick.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/usb/line6/driver.c

@@ -568,6 +568,8 @@ int line6_probe(struct usb_interface *interface,
 	return 0;
 
  err_destruct:
+	if (line6->disconnect)
+		line6->disconnect(interface);
 	snd_card_free(card);
  err_put:
 	return ret;