net: hns3: replace snprintf with scnprintf in hns3_dbg_cmd_read

mainline inclusion
from mainline-v5.6-rc1
commit 49e211c0
category: bugfix
bugzilla: NA
CVE: NA

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

The return value of snprintf may be greater than the size of
HNS3_DBG_READ_LEN, use scnprintf instead in hns3_dbg_cmd_read.

Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: Yongxin Li <liyongxin1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>