Restore find kpgd_method2 as a fallback.

Also fixes missing 'case' in switch statement.

I've got a Windows XP VM (32-bit, PAE, on Xen) that fails to initialize except with find_kpgd_method2, which does not appear to be attempted for live VMs after the latest PR.
Yes, it should probably be set to 0 before exiting with an error, but I'm trying to be explicit for the next person that has to look at this and figure out the side-effectyness of it all.

The real way to fix the side-effectyness of this part of the init would be:
* add dtb as a parameter to `method0` and `method1`
* to not to actually use `vmi->pgd` until it's been sanity checked

...but I only have time for the quick fix to restore previous functionality today.