util: fix build on non-Linux

Fix typo in virNetDevPFGetVF() stub:

  ATTRUBUTE_UNUSED -> ATTRIBUTE_UNUSED.

While here, use common indent style for arguments in
virNetDevGetVirtualFunctionIndex() stub.

src/util/virnetdev.c

@@ -1513,7 +1513,7 @@ virNetDevGetPhysicalFunction(const char *ifname ATTRIBUTE_UNUSED,
 int
 virNetDevPFGetVF(const char *pfname ATTRIBUTE_UNUSED,
                  int vf ATTRIBUTE_UNUSED,
-                 char **vfname ATTRUBUTE_UNUSED)
+                 char **vfname ATTRIBUTE_UNUSED)
 {
     virReportSystemError(ENOSYS, "%s",
                          _("Unable to get virtual function name on this platform"));