wifi: mac80211: remove unnecessary vlan NULL check

In a vlan iteration loop the vlan pointer cannot be NULL.
Remove the unnecessary check.

Link: https://patch.msgid.link/20251105161033.670b5a06296c.I24cb1a5338736ab0a8a24d6a492c259f894d09fb@changeid
Signed-off-by: Johannes Berg <[e-mail]>

net/mac80211/link.c

···
 	list_for_each_entry(vlan, &sdata->u.ap.vlans, u.vlan.list) {
 		int link_id;
 
-		if (!vlan)
-			continue;
-
 		/* No support for 4addr with MLO yet */
 		if (vlan->wdev.use_4addr)
 			return;