net: hns3: fix local variable "desc" not initialized problem

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

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

In hclge_mac_update_stats_defective(), the local variable "desc"
is not initialized, if the mac statistics returned from firmware
is less then the size of desc, will cause the rest mac statistics
are random.

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: li yongxin <liyongxin1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>