media: usb: usbtv: Stop direct calls to queue num_buffers field

JIRA: https://issues.redhat.com/browse/RHEL-86821

commit 4545ca5
Author: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Date: Thu Nov 9 17:34:58 2023 +0100

  Use vb2_get_num_buffers() to avoid using queue num_buffers field directly.
  This allows us to change how the number of buffers is computed in the
  future.

  Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
  Reviewed-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
  Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
  Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Kate Hsuan <hpa@redhat.com>

Author: Kate Hsuan

drivers/media/usb/usbtv/usbtv-video.c

@@ -726,9 +726,10 @@ static int usbtv_queue_setup(struct vb2_queue *vq,
 {
 	struct usbtv *usbtv = vb2_get_drv_priv(vq);
 	unsigned size = USBTV_CHUNK * usbtv->n_chunks * 2 * sizeof(u32);
+	unsigned int q_num_bufs = vb2_get_num_buffers(vq);
 
-	if (vq->num_buffers + *nbuffers < 2)
-		*nbuffers = 2 - vq->num_buffers;
+	if (q_num_bufs + *nbuffers < 2)
+		*nbuffers = 2 - q_num_bufs;
 	if (*nplanes)
 		return sizes[0] < size ? -EINVAL : 0;
 	*nplanes = 1;