vfio/mbochs: Fix close when multiple device FDs are open

mbochs_close() iterates over global device state and frees it. Currently
this is done every time a device FD is closed, but if multiple device FDs
are open this could corrupt other still active FDs.

Change this to use close_device() so it only runs on the last close.
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/11-v4-9ea22c5e6afb+1adf-vfio_reflck_jgg@nvidia.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

samples/vfio-mdev/mbochs.c

@@ -1278,7 +1278,7 @@ static long mbochs_ioctl(struct vfio_device *vdev, unsigned int cmd,
 	return -ENOTTY;
 }
 
-static void mbochs_close(struct vfio_device *vdev)
+static void mbochs_close_device(struct vfio_device *vdev)
 {
 	struct mdev_state *mdev_state =
 		container_of(vdev, struct mdev_state, vdev);
@@ -1396,7 +1396,7 @@ static struct attribute_group *mdev_type_groups[] = {
 };
 
 static const struct vfio_device_ops mbochs_dev_ops = {
-	.release = mbochs_close,
+	.close_device = mbochs_close_device,
 	.read = mbochs_read,
 	.write = mbochs_write,
 	.ioctl = mbochs_ioctl,