drivers/virtio/virtio_pci.c: fix error return code

Convert a nonnegative 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>
(
if@p1 (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret@p1 = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}
// </smpl>

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/virtio/virtio_pci.c

@@ -719,8 +719,10 @@ static int __devinit virtio_pci_probe(struct pci_dev *pci_dev,
 		goto out_enable_device;
 
 	vp_dev->ioaddr = pci_iomap(pci_dev, 0, 0);
-	if (vp_dev->ioaddr == NULL)
+	if (vp_dev->ioaddr == NULL) {
+		err = -ENOMEM;
 		goto out_req_regions;
+	}
 
 	pci_set_drvdata(pci_dev, vp_dev);
 	pci_set_master(pci_dev);