[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>
diff --git a/drivers/media/usb/usbvision/usbvision-video.c b/drivers/media/usb/usbvision/usbvision-video.c
index 8a43179..f67018e 100644
--- a/drivers/media/usb/usbvision/usbvision-video.c
+++ b/drivers/media/usb/usbvision/usbvision-video.c
@@ -684,7 +684,7 @@
 }
 
 static int vidioc_s_audio(struct file *file, void *fh,
-			  struct v4l2_audio *a)
+			  const struct v4l2_audio *a)
 {
 	if (a->index)
 		return -EINVAL;