libertas: fix a potential NULL pointer dereference

alloc_workqueue is not checked for errors and as a result,
a potential NULL dereference could occur.
Signed-off-by: Allen Pais <allen.pais@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/marvell/libertas/if_sdio.c

@@ -1179,6 +1179,10 @@ static int if_sdio_probe(struct sdio_func *func,
 
 	spin_lock_init(&card->lock);
 	card->workqueue = alloc_workqueue("libertas_sdio", WQ_MEM_RECLAIM, 0);
+	if (unlikely(!card->workqueue)) {
+		ret = -ENOMEM;
+		goto err_queue;
+	}
 	INIT_WORK(&card->packet_worker, if_sdio_host_to_card_worker);
 	init_waitqueue_head(&card->pwron_waitq);
 
@@ -1230,6 +1234,7 @@ static int if_sdio_probe(struct sdio_func *func,
 	lbs_remove_card(priv);
 free:
 	destroy_workqueue(card->workqueue);
+err_queue:
 	while (card->packets) {
 		packet = card->packets;
 		card->packets = card->packets->next;