vfio-mdev/samples: make mdev_fops const and static

Make this const as it is only passed to a const argument of the function
mdev_register_device. Make it static as it is not referenced in any
other file.

Structure found using Coccinelle and changes done by hand.
Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

samples/vfio-mdev/mtty.c

@@ -1413,7 +1413,7 @@ struct attribute_group *mdev_type_groups[] = {
 	NULL,
 };
 
-struct mdev_parent_ops mdev_fops = {
+static const struct mdev_parent_ops mdev_fops = {
 	.owner                  = THIS_MODULE,
 	.dev_attr_groups        = mtty_dev_groups,
 	.mdev_attr_groups       = mdev_dev_groups,