wl12xx: configure channel/band while FW is off

Initialize the channel and band from mac80211 conf even when the FW is
not yet loaded. This mitigates a bug in AP-mode where the channel was
never changed from its initial setting after FW boot and was therefore
never configured to FW.

Reported-by: Alexander Boukaty <alexanderb@ti.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>