iwlwifi: mvm: map cab_queue to real one earlier

There may be a difference between the mac80211 vif->cab_queue and
mvmvif->cab_queue, particularly with TVQM. Make the code map this
earlier, instead of first returning the mac80211 one again from
iwl_mvm_get_ctrl_vif_queue().

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>