mm/page_owner: align with pageblock_nr pages

mm/page_owner: align with pageblock_nr pages

When pfn_valid(pfn) returns false, pfn should be aligned with
pageblock_nr_pages other than MAX_ORDER_NR_PAGES in init_pages_in_zone,
because the skipped 2M may be valid pfn, as a result, early allocated
count will not be accurate.

Link: http://lkml.kernel.org/r/1468938136-24228-1-git-send-email-zhongjiang@huawei.com
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>