[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/gspca/sn9c20x.c b/drivers/media/usb/gspca/sn9c20x.c
index 4ec544f..ead9a1f 100644
--- a/drivers/media/usb/gspca/sn9c20x.c
+++ b/drivers/media/usb/gspca/sn9c20x.c
@@ -1598,7 +1598,7 @@
 }
 
 static int sd_dbg_s_register(struct gspca_dev *gspca_dev,
-			struct v4l2_dbg_register *reg)
+			const struct v4l2_dbg_register *reg)
 {
 	struct sd *sd = (struct sd *) gspca_dev;