net: hns: bug fix for return values

The return values in the first two functions mdiobus_write()
are ignored. The patch will fix it.

Signed-off-by: Qianqian Xie <xieqianqian@huawei.com>
Signed-off-by: Yisen Zhuang <Yisen.Zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>