[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/tm6000/tm6000-video.c

@@ -1401,7 +1401,7 @@ static int radio_g_audio(struct file *file, void *priv,
 }
 
 static int radio_s_audio(struct file *file, void *priv,
-					struct v4l2_audio *a)
+					const struct v4l2_audio *a)
 {
 	return 0;
 }