wifi: iwlwifi: mvm: fix NULL deref in iwl_mvm_mld_disable_txq

Check sta pointer for NULL and don't crash if it is.

Fixes: 006c152a ("wifi: iwlwifi: mvm: add support for the new STA related commands")
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/linux-wireless/20230314194113.132873ce015c.I7b12a77e5be066730762e6ceeeaa7190293c3df1@changeid/Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/mld-sta.c

@@ -227,10 +227,15 @@ static int iwl_mvm_mld_disable_txq(struct iwl_mvm *mvm,
 				   struct ieee80211_sta *sta,
 				   u16 *queueptr, u8 tid)
 {
-	struct iwl_mvm_sta *mvmsta = iwl_mvm_sta_from_mac80211(sta);
+	struct iwl_mvm_sta *mvmsta;
 	int queue = *queueptr;
 	int ret = 0;
 
+	if (!sta)
+		return -EINVAL;
+
+	mvmsta = iwl_mvm_sta_from_mac80211(sta);
+
 	if (mvm->sta_remove_requires_queue_remove) {
 		u32 cmd_id = WIDE_ID(DATA_PATH_GROUP,
 				     SCD_QUEUE_CONFIG_CMD);