net: hns3: replace snprintf with scnprintf in hns3_dbg_cmd_read

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>