virtio_ring: code cleanup in detach_buf_split

virtio_ring: code cleanup in detach_buf_split

Since the return value of vring_unmap_one_split() is exactly
vq->split.desc_extra[i].next, 'i = vq->split.desc_extra[i].next' is
redundant. Assign vring_unmap_one_split() to i instead.

Since vq->split.desc_extra is assigned to extra, use extra[i].next
instead of vq->split.desc_extra[i].next to improve readability.

No change in functionality.

Signed-off-by: zhangdongchuan <zhangdongchuan@eswincomputing.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <202511261140162936986@eswincomputing.com>