net: PHYLIB mdio fixes #2

The PHYLIB mdio code has more problems in error paths:
- mdiobus_release can be called before bus->state is set to
  MDIOBUS_REGISTERED
- mdiobus_scan allocates resources which need to be freed
- the comment is wrong, the resistors used are actually pull-ups.

Signed-off-by: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>