isdn: fix obvious cut-and-paste error in st5481_usb.c

Fix a rather obvious cut-and-paste error, where earlier code for the
controller URB got somehow mixed in with code for the interrupt URB.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/isdn/hisax/st5481_usb.c b/drivers/isdn/hisax/st5481_usb.c
index 4ada66b..427a8b0 100644
--- a/drivers/isdn/hisax/st5481_usb.c
+++ b/drivers/isdn/hisax/st5481_usb.c
@@ -342,7 +342,7 @@
 	usb_kill_urb(intr->urb);
 	kfree(intr->urb->transfer_buffer);
 	usb_free_urb(intr->urb);
-	ctrl->urb = NULL;
+	intr->urb = NULL;
 }
 
 /*