[media] v4l2: make vidioc_s_jpegcomp const

Write-only ioctls should have a const argument in the ioctl op.
Do this conversion for vidioc_s_jpegcomp.
Adding const for write-only ioctls was decided during the 2012 Media Workshop.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/usb/gspca/zc3xx.c b/drivers/media/usb/gspca/zc3xx.c
index c47ba14..77c5775 100644
--- a/drivers/media/usb/gspca/zc3xx.c
+++ b/drivers/media/usb/gspca/zc3xx.c
@@ -6883,16 +6883,11 @@
 }
 
 static int sd_set_jcomp(struct gspca_dev *gspca_dev,
-			struct v4l2_jpegcompression *jcomp)
+			const struct v4l2_jpegcompression *jcomp)
 {
 	struct sd *sd = (struct sd *) gspca_dev;
-	int ret;
 
-	ret = v4l2_ctrl_s_ctrl(sd->jpegqual, jcomp->quality);
-	if (ret)
-		return ret;
-	jcomp->quality = v4l2_ctrl_g_ctrl(sd->jpegqual);
-	return 0;
+	return v4l2_ctrl_s_ctrl(sd->jpegqual, jcomp->quality);
 }
 
 static int sd_get_jcomp(struct gspca_dev *gspca_dev,