iwlwifi: mvm: avoid crash on restart w/o reserved queues

When the firmware restarts in a situation in which any station
has no queue reserved anymore because that queue was used, the
code will crash trying to access the queue_info array at the
offset 255, which is far too big. Fix this by checking that a
queue is actually reserved before writing its status.

Fixes: 8d98ae6e

 ("iwlwifi: mvm: re-assign old queues after hw restart in dqa mode")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>