Instead of getting estimated free pages from memblock directly, we have
introduced an API, memblock_estimated_nr_free_pages(), which is more
friendly for users.
Just replace it with new API, no functional change.
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
CC: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
CC: David Hildenbrand <david@xxxxxxxxxx>
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