powerpc/thp: Don't recompute vsid and ssize in loop on invalidate

powerpc/thp: Don't recompute vsid and ssize in loop on invalidate

commit fa1f8ae80f8bb996594167ff4750a0b0a5a5bb5d upstream.

The segment identifier and segment size will remain the same in
the loop, So we can compute it outside. We also change the
hugepage_invalidate interface so that we can use it the later patch

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>