[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/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index 79784fc..8158a08 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -165,7 +165,7 @@
 	long (*ioctl)(struct v4l2_subdev *sd, unsigned int cmd, void *arg);
 #ifdef CONFIG_VIDEO_ADV_DEBUG
 	int (*g_register)(struct v4l2_subdev *sd, struct v4l2_dbg_register *reg);
-	int (*s_register)(struct v4l2_subdev *sd, struct v4l2_dbg_register *reg);
+	int (*s_register)(struct v4l2_subdev *sd, const struct v4l2_dbg_register *reg);
 #endif
 	int (*s_power)(struct v4l2_subdev *sd, int on);
 	int (*interrupt_service_routine)(struct v4l2_subdev *sd,