net: phy: xgene: disable clk on error paths

There are several error paths in xgene_mdio_probe(),
where clk is left undisabled. The patch fixes them.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>