xen/pcifront: avoid pci_frontend_enable_msix() falsely returning success

The original XenoLinux code has always had things this way, and for
compatibility reasons (in particular with a subsequent pciback
adjustment) upstream Linux should behave the same way (allowing for two
distinct error indications to be returned by the backend).
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/pci/xen-pcifront.c

@@ -290,6 +290,7 @@ static int pci_frontend_enable_msix(struct pci_dev *dev,
 		} else {
 			printk(KERN_DEBUG "enable msix get value %x\n",
 				op.value);
+			err = op.value;
 		}
 	} else {
 		dev_err(&dev->dev, "enable msix get err %x\n", err);