net: hns3: fix a bug when getting phy address from NCL_config file

Driver gets phy address from NCL_config file and uses the phy address
to initialize phydev. There are 5 bits for phy address. And C22 phy
address has 5 bits. So 0-31 are all valid address for phy. If there
is no phy, it will crash. Because driver always get a valid phy address.

This patch fixes the phy address to 8 bits, and use 0xff to indicate
invalid phy address.

Fixes: 46a3df9f (net: hns3: Add HNS3 Acceleration Engine & Compatibility Layer Support)
Signed-off-by: Fuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: Lipeng <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>