asus/f2a85-m: Switch off automatic fan control for fan2

The fan2 (chasis fan) was set to automatic mode, but the
registers for smart guardian have still default value which
will stop it. Run it in manual mode for now.

Change-Id: Ic2c2414ac88abba77a9e7a129788f9777e7e5ad5
Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Reviewed-on: http://review.coreboot.org/6217
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>