We were registering our slave MDIO bus with OF and doing so with
assigning the newly created slave_mii_bus of_node to the master MDIO bus
controller node. This is a bad thing to do for a number of reasons:

- we are completely lying about the slave MII bus is arranged and yet we
  still want to control which MDIO devices it probes. It was attempted
  before to play tricks with the bus_mask to perform that:
  https://www.spinics.net/lists/netdev/msg429420.html but the approach
  was rightfully rejected

- the device_node reference counting is messed up and we are effectively
  doing a double probe on the devices we already probed using the
  master, this messes up all resources reference counts (such as clocks)

The proper fix for this as indicated by David in his reply to the
thread above is to use a platform data style registration so as to
control exactly which devices we probe:
https://www.spinics.net/lists/netdev/msg430083.html

By using mdiobus_register(), our slave_mii_bus->phy_mask value is used
as intended, and all the PHY addresses that must be redirected towards
our slave MDIO bus is happening while other addresses get redirected
towards the master MDIO bus.

Fixes: 461cd1b0 ("net: dsa: bcm_sf2: Register our slave MDIO bus")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>