[media] stk1160: Replace BUG_ON with WARN_ON

This situation is not even an error condition so it's stupid to BUG_ON.
Learn the lesson:
http://permalink.gmane.org/gmane.linux.kernel/1347333

Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/usb/stk1160/stk1160-video.c

@@ -78,7 +78,7 @@ struct stk1160_buffer *stk1160_next_buffer(struct stk1160 *dev)
 	unsigned long flags = 0;
 
 	/* Current buffer must be NULL when this functions gets called */
-	BUG_ON(dev->isoc_ctl.buf);
+	WARN_ON(dev->isoc_ctl.buf);
 
 	spin_lock_irqsave(&dev->buf_lock, flags);
 	if (!list_empty(&dev->avail_bufs)) {