net: dsa: bcm_sf2: Fix unbind ordering

The order in which we release resources is unfortunately leading to bus
errors while dismantling the port. This is because we set
priv->wol_ports_mask to 0 to tell bcm_sf2_sw_suspend() that it is now
permissible to clock gate the switch. Later on, when dsa_slave_destroy()
comes in from dsa_unregister_switch() and calls
dsa_switch_ops::port_disable, we perform the same dismantling again, and
this time we hit registers that are clock gated.

Make sure that dsa_unregister_switch() is the first thing that happens,
which takes care of releasing all user visible resources, then proceed
with clock gating hardware. We still need to set priv->wol_ports_mask to
0 to make sure that an enabled port properly gets disabled in case it
was previously used as part of Wake-on-LAN.

Fixes: d9338023

 ("net: dsa: bcm_sf2: Make it a real platform device driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>