wifi: mt76: mt7915: Fix an error handling path in mt7915_add_interface()

If mt76_wcid_alloc() fails, the "mt76.mutex" mutex needs to be released as
done in the other error handling paths of mt7915_add_interface().

Fixes: f3049b8 ("wifi: mt76: mt7915: allocate vif wcid in the same range as stations")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/b9d8fbfc19360bfe60b9cea1cb0f735ab3b4bc26.1727639596.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Felix Fietkau <nbd@nbd.name>

Author: tititiou36

drivers/net/wireless/mediatek/mt76/mt7915/main.c

@@ -246,8 +246,10 @@ static int mt7915_add_interface(struct ieee80211_hw *hw,
 	phy->omac_mask |= BIT_ULL(mvif->mt76.omac_idx);
 
 	idx = mt76_wcid_alloc(dev->mt76.wcid_mask, mt7915_wtbl_size(dev));
-	if (idx < 0)
-		return -ENOSPC;
+	if (idx < 0) {
+		ret = -ENOSPC;
+		goto out;
+	}
 
 	INIT_LIST_HEAD(&mvif->sta.rc_list);
 	INIT_LIST_HEAD(&mvif->sta.wcid.poll_list);