net: phylink: Convert some users of mdiobus_* to mdiodev_*

This refactors the phylink pcs helper functions to use mdiobus_* instead
of mdiodev_*.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>