media: v4l2-pci-skeleton: constify vb2_ops structures

These vb2_ops structures are only stored in the ops field of a
vb2_queue structure, which is declared as const.  Thus the vb2_ops
structures themselves can be const.

Done with the help of Coccinelle.

// <smpl>
@r disable optional_qualifier@
identifier i;
position p;
@@
static struct vb2_ops i@p = { ... };

@ok@
identifier r.i;
struct vb2_queue e;
position p;
@@
e.ops = &i@p;

@bad@
position p != {r.p,ok.p};
identifier r.i;
struct vb2_ops e;
@@
e@i@p

@depends on !bad disable optional_qualifier@
identifier r.i;
@@
static
+const
 struct vb2_ops i = { ... };
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

samples/v4l/v4l2-pci-skeleton.c

@@ -282,7 +282,7 @@ static void stop_streaming(struct vb2_queue *vq)
  * vb2_ops_wait_prepare/finish helper functions. If q->lock would be NULL,
  * then this driver would have to provide these ops.
  */
-static struct vb2_ops skel_qops = {
+static const struct vb2_ops skel_qops = {
 	.queue_setup		= queue_setup,
 	.buf_prepare		= buffer_prepare,
 	.buf_queue		= buffer_queue,