virtio_ring: fix num_free handling in error case

commit e82df670 upstream.

The vq->vq.num_free hasn't been changed when error happens,
so it shouldn't be changed when handling the error.

Fixes: 780bc790 ("virtio_ring: Support DMA APIs")
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/virtio/virtio_ring.c

@@ -423,8 +423,6 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 		i = vq->vring.desc[i].next;
 	}
 
-	vq->vq.num_free += total_sg;
-
 	if (indirect)
 		kfree(desc);