[media] v4l2: make vidioc_s_modulator const

Write-only ioctls should have a const argument in the ioctl op.
Do this conversion for vidioc_s_modulator.
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>

drivers/media/radio/radio-keene.c

@@ -203,7 +203,7 @@ static int vidioc_g_modulator(struct file *file, void *priv,
 }
 
 static int vidioc_s_modulator(struct file *file, void *priv,
-				struct v4l2_modulator *v)
+				const struct v4l2_modulator *v)
 {
 	struct keene_device *radio = video_drvdata(file);