drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c: add missing iounmap

Add missing iounmap in error handling code, in a case where the function
already preforms iounmap on some other execution path.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression e;
statement S,S1;
int ret;
@@
e = \(ioremap\|ioremap_nocache\)(...)
... when != iounmap(e)
if (<+...e...+>) S
... when any
    when != iounmap(e)
*if (...)
   { ... when != iounmap(e)
     return ...; }
... when any
iounmap(e);
// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c

@@ -62,7 +62,7 @@ static int stmmac_pltfr_probe(struct platform_device *pdev)
 	priv = stmmac_dvr_probe(&(pdev->dev), plat_dat);
 	if (!priv) {
 		pr_err("%s: main drivr probe failed", __func__);
-		goto out_release_region;
+		goto out_unmap;
 	}
 
 	priv->ioaddr = addr;