[media] vb2: Fix compilation breakage when !CONFIG_BUG

Commit 77a3c6fd ("[media] vb2: Don't WARN when v4l2_buffer.bytesused
is 0 for multiplanar buffers") uses the __WARN() macro which isn't
defined when CONFIG_BUG isn't set. This introduces a compilation
breakage. Fix it by using WARN_ON() instead.

The commit was also broken in that it merged v1 of the patch while a new
v2 version had been submitted, reviewed and acked. Fix it by
incorporating the changes from v1 to v2.

Fixes: 77a3c6fd ("[media] vb2: Don't WARN when v4l2_buffer.bytesused is 0 for multiplanar buffers")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

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

@@ -1254,19 +1254,19 @@ EXPORT_SYMBOL_GPL(vb2_discard_done);
 
 static void vb2_warn_zero_bytesused(struct vb2_buffer *vb)
 {
-	static bool __check_once __read_mostly;
+	static bool check_once;
 
-	if (__check_once)
+	if (check_once)
 		return;
 
-	__check_once = true;
-	__WARN();
+	check_once = true;
+	WARN_ON(1);
 
-	pr_warn_once("use of bytesused == 0 is deprecated and will be removed in the future,\n");
+	pr_warn("use of bytesused == 0 is deprecated and will be removed in the future,\n");
 	if (vb->vb2_queue->allow_zero_bytesused)
-		pr_warn_once("use VIDIOC_DECODER_CMD(V4L2_DEC_CMD_STOP) instead.\n");
+		pr_warn("use VIDIOC_DECODER_CMD(V4L2_DEC_CMD_STOP) instead.\n");
 	else
-		pr_warn_once("use the actual size instead.\n");
+		pr_warn("use the actual size instead.\n");
 }
 
 /**