[media] v4l2: make vidioc_s_fbuf const

Write-only ioctls should have a const argument in the ioctl op.
Do this conversion for vidioc_s_fbuf.
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 b58ff87..26bf309 100644
--- a/drivers/media/pci/bt8xx/bttv-driver.c
+++ b/drivers/media/pci/bt8xx/bttv-driver.c
@@ -2740,7 +2740,7 @@
 }
 
 static int bttv_s_fbuf(struct file *file, void *f,
-				struct v4l2_framebuffer *fb)
+				const struct v4l2_framebuffer *fb)
 {
 	struct bttv_fh *fh = f;
 	struct bttv *btv = fh->btv;