staging: wfx: detect race condition in WEP authentication

Current code has a special case to handle association with WEP. Before
to rework the tx data handling, let's try to detect any possible misuse
of this code.
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191217161318.31402-9-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/queue.c

@@ -422,6 +422,7 @@ static bool hif_handle_tx_data(struct wfx_vif *wvif, struct sk_buff *skb,
 		break;
 	case do_wep:
 		wfx_tx_lock(wvif->wdev);
+		WARN_ON(wvif->wep_pending_skb);
 		wvif->wep_default_key_id = tx_priv->hw_key->keyidx;
 		wvif->wep_pending_skb = skb;
 		if (!schedule_work(&wvif->wep_key_work))