powerpc, memblock: Fix memblock API change fallout

Fix memblock API change fallout in the WII code.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: linux-mm@kvack.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
LKML-Reference: <4C8B2AFA.2000705@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>