[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/radio/radio-sf16fmi.c b/drivers/media/radio/radio-sf16fmi.c
index 8185d5f..227dcdb5 100644
--- a/drivers/media/radio/radio-sf16fmi.c
+++ b/drivers/media/radio/radio-sf16fmi.c
@@ -239,7 +239,7 @@
 }
 
 static int vidioc_s_audio(struct file *file, void *priv,
-					struct v4l2_audio *a)
+					const struct v4l2_audio *a)
 {
 	return a->index ? -EINVAL : 0;
 }