media: videobuf2-v4l2: drop WARN_ON in vb2_warn_zero_bytesused()

Userspace shouldn't set bytesused to 0 for output buffers.
vb2_warn_zero_bytesused() warns about this (only once!), but it also
calls WARN_ON(1), which is confusing since it is not immediately clear
that it warns about a 0 value for bytesused.

Just drop the WARN_ON as it serves no purpose.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

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

@@ -158,7 +158,6 @@ static void vb2_warn_zero_bytesused(struct vb2_buffer *vb)
 		return;
 
 	check_once = true;
-	WARN_ON(1);
 
 	pr_warn("use of bytesused == 0 is deprecated and will be removed in the future,\n");
 	if (vb->vb2_queue->allow_zero_bytesused)