media: pci: cx18: Stop direct calls to queue num_buffers field

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>
CC: Sergey Kozlov <serjk@netup.ru>
CC: Abylay Ospan <aospan@netup.ru>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/pci/cx18/cx18-streams.c

@@ -104,6 +104,7 @@ static int cx18_queue_setup(struct vb2_queue *vq,
 			    unsigned int *nbuffers, unsigned int *nplanes,
 			    unsigned int sizes[], struct device *alloc_devs[])
 {
+	unsigned int q_num_bufs = vb2_get_num_buffers(vq);
 	struct cx18_stream *s = vb2_get_drv_priv(vq);
 	struct cx18 *cx = s->cx;
 	unsigned int szimage;
@@ -121,8 +122,8 @@ static int cx18_queue_setup(struct vb2_queue *vq,
 	 * Let's request at least three buffers: two for the
 	 * DMA engine and one for userspace.
 	 */
-	if (vq->num_buffers + *nbuffers < 3)
-		*nbuffers = 3 - vq->num_buffers;
+	if (q_num_bufs + *nbuffers < 3)
+		*nbuffers = 3 - q_num_bufs;
 
 	if (*nplanes) {
 		if (*nplanes != 1 || sizes[0] < szimage)