util: fix build mingw (and all non-linux) build failure

ATTRIBUTE_UNUSED was accidentally forgotten on one arg of a stub
function for functionality that's not present on non-linux
platforms. This causes a non-linux build with
--enable-compile-warnings=error to fail.

src/util/pci.c

@@ -2219,7 +2219,8 @@ pciDeviceNetName(char *device_link_sysfs_path ATTRIBUTE_UNUSED,
 
 int
 pciDeviceGetVirtualFunctionInfo(const char *vf_sysfs_device_path ATTRIBUTE_UNUSED,
-                                char **pfname, int *vf_index ATTRIBUTE_UNUSED)
+                                char **pfname ATTRIBUTE_UNUSED,
+                                int *vf_index ATTRIBUTE_UNUSED)
 {
     pciReportError(VIR_ERR_INTERNAL_ERROR, _("pciDeviceGetVirtualFunctionInfo "
                    "is not supported on non-linux platforms"));