net: mvmdio: allow up to four clocks to be specified for orion-mdio

Allow up to four clocks to be specified and enabled for the orion-mdio
interface, which are required by the Armada 8k and defined in
armada-cp110.dtsi.

Fixes a hang in probing the mvmdio driver that was encountered on the
Clearfog GT 8K with all drivers built as modules, but also affects other
boards such as the MacchiatoBIN.

Cc: stable@vger.kernel.org
Fixes: 96cb4342 ("net: mvmdio: allow up to three clocks to be specified for orion-mdio")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Josua Mayer <josua@solid-run.com>
Signed-off-by: David S. Miller <davem@davemloft.net>