rsi: fix memory leak on failed URB submission

Make sure to free the skb on failed receive-URB submission (e.g. on
disconnect or currently also due to a missing endpoint).

Fixes: a1854fae ("rsi: improve RX packet handling in USB interface")
Cc: stable <stable@vger.kernel.org>     # 4.17
Cc: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/rsi/rsi_91x_usb.c

@@ -338,8 +338,10 @@ static int rsi_rx_urb_submit(struct rsi_hw *adapter, u8 ep_num)
 			  rx_cb);
 
 	status = usb_submit_urb(urb, GFP_KERNEL);
-	if (status)
+	if (status) {
 		rsi_dbg(ERR_ZONE, "%s: Failed in urb submission\n", __func__);
+		dev_kfree_skb(skb);
+	}
 
 	return status;
 }