iwlwifi: fix multi queue notification for a000 devices

Currently we return early from sync_rx_queues for a000 devices.
This may cause, in case of a non-empty reorder buffer, a warning
later on since the RX queue isn't getting the notification to
empty it.
A better approach would be to send the notification for the default
queue only.
Do this hard coded for now, until we will have the API to enable
multi queue for a000 devices.

Fixes: bc029469 ("iwlwifi: mvm: disable RX queue notification for a000 devices")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>