[media] videobuf2-core: Replace BUG_ON and return an error at vb2_queue_init()

This replaces BUG_ON() calls with WARN_ON(), and returns
EINVAL if some parameter is NULL, as suggested by Jonathan and Mauro.
The BUG_ON() call is too drastic to be used in this case.
See the full discussion here:
http://www.spinics.net/lists/linux-media/msg52462.html

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

drivers/media/v4l2-core/videobuf2-core.c

@@ -1738,14 +1738,17 @@ EXPORT_SYMBOL_GPL(vb2_poll);
  */
 int vb2_queue_init(struct vb2_queue *q)
 {
-	BUG_ON(!q);
-	BUG_ON(!q->ops);
-	BUG_ON(!q->mem_ops);
-	BUG_ON(!q->type);
-	BUG_ON(!q->io_modes);
-
-	BUG_ON(!q->ops->queue_setup);
-	BUG_ON(!q->ops->buf_queue);
+	/*
+	 * Sanity check
+	 */
+	if (WARN_ON(!q)			  ||
+	    WARN_ON(!q->ops)		  ||
+	    WARN_ON(!q->mem_ops)	  ||
+	    WARN_ON(!q->type)		  ||
+	    WARN_ON(!q->io_modes)	  ||
+	    WARN_ON(!q->ops->queue_setup) ||
+	    WARN_ON(!q->ops->buf_queue))
+		return -EINVAL;
 
 	INIT_LIST_HEAD(&q->queued_list);
 	INIT_LIST_HEAD(&q->done_list);

include/media/videobuf2-core.h

@@ -324,7 +324,7 @@ int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req);
 int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create);
 int vb2_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b);
 
-int vb2_queue_init(struct vb2_queue *q);
+int __must_check vb2_queue_init(struct vb2_queue *q);
 
 void vb2_queue_release(struct vb2_queue *q);