phy: fix blackfin build failure

The build of blackfin defconfig is failing with the error:
error: 'struct mii_bus' has no member named 'phy_map'

A new API mdiobus_get_phy() was introduced and phy_map was removed but
it was not changed here.

Fixes: 7f854420

 ("phy: Add API for {un}registering an mdio device to a bus.")
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>