c/s 45ac805 "x86/paging: Package up the log dirty function pointers" neglected
the case when CONFIG_SHADOW_PAGING is disabled. Make a similar adjustment to
the none stubs.
Spotted by a Travis RANDCONFIG run.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: Tim Deegan <tim@xen.org>