wifi: mt76: mt7996: prevent uninit return in mt7996_mac_sta_add_links

If link_conf_dereference_protected() or mt7996_vif_link()
or link_sta_dereference_protected() fail the code jumps to
the error_unlink label and returns ret which is uninitialised.

Fix this by setting err before jumping to error_unlink.

Fixes: c7e4fc3 ("wifi: mt76: mt7996: Update mt7996_mcu_add_sta to MLO support")
Fixes: dd82a9e ("wifi: mt76: mt7996: Rely on mt7996_sta_link in sta_add/sta_remove callbacks")
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
Link: https://patch.msgid.link/20250421110550.9839-1-qasdev00@gmail.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>

Author: qasim-ijaz

drivers/net/wireless/mediatek/mt76/mt7996/main.c

@@ -998,16 +998,22 @@ mt7996_mac_sta_add_links(struct mt7996_dev *dev, struct ieee80211_vif *vif,
 			continue;
 
 		link_conf = link_conf_dereference_protected(vif, link_id);
-		if (!link_conf)
+		if (!link_conf) {
+			err = -EINVAL;
 			goto error_unlink;
+		}
 
 		link = mt7996_vif_link(dev, vif, link_id);
-		if (!link)
+		if (!link) {
+			err = -EINVAL;
 			goto error_unlink;
+		}
 
 		link_sta = link_sta_dereference_protected(sta, link_id);
-		if (!link_sta)
+		if (!link_sta) {
+			err = -EINVAL;
 			goto error_unlink;
+		}
 
 		err = mt7996_mac_sta_init_link(dev, link_conf, link_sta, link,
 					       link_id);