net: mvmdio: print warning when orion-mdio has too many clocks

Print a warning when device tree specifies more than the maximum of four
clocks supported by orion-mdio. Because reading from mdio can lock up
the Armada 8k when a required clock is not initialized, it is important
to notify the user when a specified clock is ignored.

Signed-off-by: Josua Mayer <josua@solid-run.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>