The switch may want to instantiate its own MDIO bus. Only do it
centrally if the switch has not already created one, and the read op
is implemented.
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>