net: ethernet: Fix memleak in ethoc_probe

When mdiobus_register() fails, priv->mdio allocated
by mdiobus_alloc() has not been freed, which leads
to memleak.

Fixes: e7f4dc3536a4 ("mdio: Move allocation of interrupts into core")
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20201223110615.31389-1-dinghao.liu@zju.edu.cn


Signed-off-by: Jakub Kicinski <kuba@kernel.org>