[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/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c
index 4b9a256..e33a2d2 100644
--- a/drivers/media/pci/bt8xx/bttv-driver.c
+++ b/drivers/media/pci/bt8xx/bttv-driver.c
@@ -1945,7 +1945,7 @@
 }
 
 static int bttv_s_register(struct file *file, void *f,
-					struct v4l2_dbg_register *reg)
+					const struct v4l2_dbg_register *reg)
 {
 	struct bttv_fh *fh = f;
 	struct bttv *btv = fh->btv;
@@ -1961,8 +1961,7 @@
 	}
 
 	/* bt848 has a 12-bit register space */
-	reg->reg &= 0xfff;
-	btwrite(reg->val, reg->reg);
+	btwrite(reg->val, reg->reg & 0xfff);
 
 	return 0;
 }