iwlwifi: mvm: avoid possible NULL pointer dereference

When adding a PASN station, the station is added to the list only
if a TK is configured. Otherwise the station pointer should not be
used.
Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201008180656.b8a493c168a7.Ie9a0f9dfd9e9c58c603dd06e45151119467a7804@changeid

drivers/net/wireless/intel/iwlwifi/mvm/ftm-responder.c

@@ -354,18 +354,16 @@ int iwl_mvm_ftm_respoder_add_pasn_sta(struct iwl_mvm *mvm,
 			kfree(sta);
 			return ret;
 		}
+
+		memcpy(sta->addr, addr, ETH_ALEN);
+		list_add_tail(&sta->list, &mvm->resp_pasn_list);
 	}
 
 	ret = iwl_mvm_ftm_responder_dyn_cfg_v3(mvm, vif, NULL, &hltk_data);
-	if (ret) {
-		if (sta)
-			iwl_mvm_resp_del_pasn_sta(mvm, vif, sta);
-		return ret;
-	}
+	if (ret && sta)
+		iwl_mvm_resp_del_pasn_sta(mvm, vif, sta);
 
-	memcpy(sta->addr, addr, ETH_ALEN);
-	list_add_tail(&sta->list, &mvm->resp_pasn_list);
-	return 0;
+	return ret;
 }
 
 int iwl_mvm_ftm_resp_remove_pasn_sta(struct iwl_mvm *mvm,