net: hns3: fix memory override when bd_num is bigger than the ring size

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

----------------------------

The bd_num is from firmware, it may be bigger than the ring
size, and may cause memory override problem.

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: Junxin Chen <chenjunxin1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>