net: hns: fixes no syscon error when init mdio

As dtsi files use the normal naming conventions using '-' instead of '_'
inside of property names, the driver needs to update the phandle name
strings of the of_parse_phandle func.

Signed-off-by: Kejian Yan <yankejian@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>