[rtl818x] Fix resource leak on error path

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/rtl818x/rtl818x.c

 	hwinfo = zalloc(sizeof(*hwinfo));
 	if (!hwinfo) {
 		DBG("rtl818x: hwinfo alloc failed\n");
-		return -ENOMEM;
+		err = -ENOMEM;
+		goto err_alloc_hwinfo;
 	}
 
 	adjust_pci_device(pdev);
 	dev = net80211_alloc(sizeof(*priv));
 	if (!dev) {
 		DBG("rtl818x: net80211 alloc failed\n");
-		return -ENOMEM;
+		err = -ENOMEM;
+		goto err_alloc_dev;
 	}
 
 	priv = dev->priv;
  err_free_dev:
 	pci_set_drvdata(pdev, NULL);
 	net80211_free(dev);
+ err_alloc_dev:
 	free(hwinfo);
+ err_alloc_hwinfo:
 	return err;
 }