net: hns3: rename hns_nic_dma_unmap

To keep symmetrical, this patch renames hns_nic_dma_unmap to
hns3_clear_desc.

Signed-off-by: Fuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>