V4L/DVB (11991): buf-core.c: add pointer check

add poiter check for videobuf_queue_core_init().

any guys who write a v4l driver, pass a NULL pointer or a non-inintial
pointer to the first parameter such as videobuf_queue_sg_init() , it
would be crashed.
Signed-off-by: Figo.zhang <figo1802@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/videobuf-core.c

@@ -118,6 +118,7 @@ void videobuf_queue_core_init(struct videobuf_queue *q,
 			 void *priv,
 			 struct videobuf_qtype_ops *int_ops)
 {
+	BUG_ON(!q);
 	memset(q, 0, sizeof(*q));
 	q->irqlock   = irqlock;
 	q->dev       = dev;