ibm/emac: fix improper cleanup when device is removed to allow re-bind

The re-binding (unbind..bind) of an EMAC device fails because the
static variable "busy_phy_map" is not updated when the device is
removed.

Signed-off-by: Wolfgang Grandegger <wg@denx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>