[media] v4l2: make vidioc_s_audio const

Write-only ioctls should have a const argument in the ioctl op.
Do this conversion for vidioc_s_audio.
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/usb/hdpvr/hdpvr-video.c

@@ -677,7 +677,7 @@ static int vidioc_enumaudio(struct file *file, void *priv,
 }
 
 static int vidioc_s_audio(struct file *file, void *private_data,
-			  struct v4l2_audio *audio)
+			  const struct v4l2_audio *audio)
 {
 	struct hdpvr_fh *fh = file->private_data;
 	struct hdpvr_device *dev = fh->dev;