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

Armada 8040 needs three clocks to be enabled for MDIO accesses to work.
Update the binding to allow the extra clocks to be specified.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -14,7 +14,7 @@ Required properties:
 
 Optional properties:
 - interrupts: interrupt line number for the SMI error/done interrupt
-- clocks: Phandle to the clock control device and gate bit
+- clocks: phandle for up to three 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