drivers: net: xgene-v2: Fix error return code in xge_mdio_config()

Fix to return error code -ENODEV from the no PHY found error
handling case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>