KVM: PPC: Book3S HV: Make H_REMOVE return correct HPTE value for absent HPTEs

KVM: PPC: Book3S HV: Make H_REMOVE return correct HPTE value for absent HPTEs

This fixes a bug where the old HPTE value returned by H_REMOVE has
the valid bit clear if the HPTE was an absent HPTE, as happens for
HPTEs for emulated MMIO pages and for RAM pages that have been paged
out by the host.  If the absent bit is set, we clear it and set the
valid bit, because from the guest's point of view, the HPTE is valid.

Signed-off-by: Paul Mackerras <paulus@samba.org>