net: hns3: optimize the barrier using when cleaning TX BD

Currently, a barrier is used when cleaning each TX BD, which may
cause performance degradation.

This patch optimizes it to use one barrier when cleaning TX BD
each round.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>