[media] v4l2: add const to argument of write-only s_register ioctl

This ioctl is defined as IOW, so pass the argument as const.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/usb/cx231xx/cx231xx-video.c b/drivers/media/usb/cx231xx/cx231xx-video.c
index 4cff2f4..cd22147 100644
--- a/drivers/media/usb/cx231xx/cx231xx-video.c
+++ b/drivers/media/usb/cx231xx/cx231xx-video.c
@@ -1404,7 +1404,7 @@
 }
 
 int cx231xx_s_register(struct file *file, void *priv,
-			     struct v4l2_dbg_register *reg)
+			     const struct v4l2_dbg_register *reg)
 {
 	struct cx231xx_fh *fh = priv;
 	struct cx231xx *dev = fh->dev;