net: dsa: bcm_sf2: Move setup function at the far end

Re-order the bcm_sf2_sw_setup() function so that it is at the far end of
the driver to avoid any kind of forward declarations.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>