net: hns3: fix shaper parameter algorithm

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

HNS3 driver use unsigned int to calculate the shaper parameter,
when the configured bandwidth is small, like 1M, the actual result
is 1.28M in the chip side. This bug only appears when the bandwidth
is less than 20M.

This patch plus the ir_s one more time when the calculated result
is equals to the configured bandwidth, so that can get a value
closer to the configured bandwidth.

Feature or Bugfix:Bugfix

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: linyunsheng <linyunsheng@huawei.com>
Reviewed-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>