rtl818x: pci_iomap() should pair with pci_iounmap()

Currently the driver uses pci_iomap() but iounmap() is called in
the error path

Change to use pci_iounmap() instead.
Reported-by: Huqiu Liu <liuhq11@mails.tsinghua.edu.cn>
Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtl818x/rtl8180/dev.c

@@ -1137,7 +1137,7 @@ static int rtl8180_probe(struct pci_dev *pdev,
 	return 0;
 
  err_iounmap:
-	iounmap(priv->map);
+	pci_iounmap(pdev, priv->map);
 
  err_free_dev:
 	ieee80211_free_hw(dev);