net: hns: set correct return value

The function of_parse_phandle() returns a NULL pointer if it cannot
resolve a phandle property to a device_node pointer. In function
hns_nic_dev_probe(), its return value is passed to PTR_ERR to extract
the error code. However, in this case, the extracted error code will
always be zero, which is unexpected.

Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>