virtio_ring: fix num_free handling in error case

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

Fixes: 780bc79 ("virtio_ring: Support DMA APIs")
Cc: Andy Lutomirski <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: [email protected]
Signed-off-by: Tiwei Bie <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>

Author: Tiwei Bie

drivers/virtio/virtio_ring.c

@@ -428,8 +428,6 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 		i = virtio16_to_cpu(_vq->vdev, vq->vring.desc[i].next);
 	}
 
-	vq->vq.num_free += total_sg;
-
 	if (indirect)
 		kfree(desc);