carl9170: fix init-self regression

The commit: "carl9170: tx path review" introduced a regression.

gcc (with -Winit-self):
tx.c:1264: warning: ‘super’ is used uninitialized in this function
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/carl9170/tx.c

@@ -1261,7 +1261,7 @@ static void carl9170_tx(struct ar9170 *ar)
 static bool carl9170_tx_ampdu_queue(struct ar9170 *ar,
 	struct ieee80211_sta *sta, struct sk_buff *skb)
 {
-	struct _carl9170_tx_superframe *super = (void *) super;
+	struct _carl9170_tx_superframe *super = (void *) skb->data;
 	struct carl9170_sta_info *sta_info;
 	struct carl9170_sta_tid *agg;
 	struct sk_buff *iter;