net: dsa: Fix use after free in dsa_switch_remove()

The order in which the ports are deleted from the list and freed and the
call to dsa_switch_remove() is done is reversed, which leads to an
use after free condition. Reverse the two: first tear down the ports and
switch from the fabric, then free the ports associated with that switch
fabric.

Fixes: 05f294a8

 ("net: dsa: allocate ports on touch")
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>