iwlwifi: mvm: don't free queue after delba in dqa

In DQA mode, a delBA might free the queue although it
shouldn't. Fix that.

Fixes: cf941e174ee2 ("iwlwifi: mvm: support dqa-mode agg on non-shared queue")
Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>