wifi: mac80211: clarify vif handling in TX dequeue

The vif pointer at least looks like it can actually be NULL
in some cases such as the monitor-mode vif, causing static
checkers to complain with the immediate derefence. In these
cases the sta pointer will also be NULL, but clarify it in
the code anyway.

Link: https://msgid.link/20240131164910.60066625a239.Idfb6a5a9876f9f631eae760055e1c4018259a971@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -3953,7 +3953,8 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
 			ieee80211_free_txskb(&local->hw, skb);
 			goto begin;
 		} else {
-			vif = NULL;
+			info->control.vif = NULL;
+			return skb;
 		}
 		break;
 	case NL80211_IFTYPE_AP_VLAN: