[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>
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 59ed522..e6a26b4 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -1738,14 +1738,17 @@
  */
 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);