[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/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c
index 26bf309..31b2826 100644
--- a/drivers/media/pci/bt8xx/bttv-driver.c
+++ b/drivers/media/pci/bt8xx/bttv-driver.c
@@ -3076,7 +3076,7 @@
 	return 0;
 }
 
-static int bttv_s_audio(struct file *file, void *priv, struct v4l2_audio *a)
+static int bttv_s_audio(struct file *file, void *priv, const struct v4l2_audio *a)
 {
 	if (unlikely(a->index))
 		return -EINVAL;
@@ -3480,7 +3480,7 @@
 }
 
 static int radio_s_audio(struct file *file, void *priv,
-					struct v4l2_audio *a)
+					const struct v4l2_audio *a)
 {
 	if (unlikely(a->index))
 		return -EINVAL;