mm/page_alloc: fix incorrect PGFREE and PGALLOC for high-order page

mm/page_alloc: fix incorrect PGFREE and PGALLOC for high-order page

PGFREE and PGALLOC represent the number of freed and allocated pages.  So
the page order must be considered.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
Signed-off-by: Yafang Shao <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Reviewed-by: Miaohe Lin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>