virtio-ring: fix DMA metadata flags

The flags are currently overwritten, leading to the wrong direction
being passed to the DMA unmap functions.

Fixes: 72b5e89 ("virtio-ring: store DMA metadata in desc_extra for split virtqueue")
Signed-off-by: Vincent Whitchurch <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Michael S. Tsirkin <[email protected]>
Acked-by: Jason Wang <[email protected]>

Author: vwax

drivers/virtio/virtio_ring.c

@@ -576,7 +576,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	/* Last one doesn't continue. */
 	desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
 	if (!indirect && vq->use_dma_api)
-		vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags =
+		vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=
 			~VRING_DESC_F_NEXT;
 
 	if (indirect) {