drivers: net: phy: xgene: Remove redundant dev_err call in xgene_mdio_probe()

There is a error message within devm_ioremap_resource
already, so remove the dev_err call to avoid redundant
error message.

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Acked-By: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>