dt-bindings: allow up to four clocks for orion-mdio

Armada 8040 needs four clocks to be enabled for MDIO accesses to work.
Update the binding to allow the extra clock to be specified.

Cc: stable@vger.kernel.org
Fixes: 6d6a331f ("dt-bindings: allow up to three clocks for orion-mdio")
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NJosua Mayer <josua@solid-run.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/marvell-orion-mdio.txt

@@ -16,7 +16,7 @@ Required properties:
 
 Optional properties:
 - interrupts: interrupt line number for the SMI error/done interrupt
-- clocks: phandle for up to three required clocks for the MDIO instance
+- clocks: phandle for up to four required clocks for the MDIO instance
 
 The child nodes of the MDIO driver are the individual PHY devices
 connected to this MDIO bus. They must have a "reg" property given the