net: hns3: use dma_zalloc_coherent instead of kzalloc/dma_map_single

Reference to Documentation/DMA-API-HOWTO.txt,
Streaming DMA mappings which are usually mapped for one DMA transfer,
Network card DMA ring descriptors should use Consistent DMA mappings.

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>