drivers/tty/moxa.c: fix error return code

Convert a 0 error return code to a negative one, as returned elsewhere in the
function.

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

// <smpl>
@@
identifier ret;
expression e,e1,e2,e3,e4,x;
@@

(
if (\(ret != 0\|ret < 0\) || ...) { ... return ...; }
|
ret = 0
)
... when != ret = e1
*x = \(kmalloc\|kzalloc\|kcalloc\|devm_kzalloc\|ioremap\|ioremap_nocache\|devm_ioremap\|devm_ioremap_nocache\)(...);
... when != x = e2
    when != ret = e3
*if (x == NULL || ...)
{
  ... when != ret = e4
*  return ret;
}
// </smpl>
Signed-off-by: NJulia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/moxa.c

@@ -977,6 +977,7 @@ static int __devinit moxa_pci_probe(struct pci_dev *pdev,
 	board->basemem = ioremap_nocache(pci_resource_start(pdev, 2), 0x4000);
 	if (board->basemem == NULL) {
 		dev_err(&pdev->dev, "can't remap io space 2\n");
+		retval = -ENOMEM;
 		goto err_reg;
 	}