cma: decrease cc.nr_migratepages after reclaiming pagelist

cma: decrease cc.nr_migratepages after reclaiming pagelist

reclaim_clean_pages_from_list() reclaims clean pages before migration so
cc.nr_migratepages should be updated.  Currently, there is no problem but
it can be wrong if we try to use the value in future.

Signed-off-by: Minchan Kim <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Cc: Michal Nazarewicz <[email protected]>
Cc: Bartlomiej Zolnierkiewicz <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>