xgene-v2: Fix a resource leak in the error handling path of 'xge_probe()'

A successful 'xge_mdio_config()' call should be balanced by a corresponding
'xge_mdio_remove()' call in the error handling path of the probe, as
already done in the remove function.

Update the error handling path accordingly.

Fixes: ea8ab16a

 ("drivers: net: xgene-v2: Add MDIO support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>