mm/compaction.c: clean code by removing unnecessary assignment

Previously 0 was assigned to variable 'last_migrated_pfn'.  But the
variable is not read after that, so the assignment can be removed.
Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Link: http://lkml.kernel.org/r/20200318174509.15021-1-mateusznosek0@gmail.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/compaction.c

@@ -2182,7 +2182,6 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 			ret = COMPACT_CONTENDED;
 			putback_movable_pages(&cc->migratepages);
 			cc->nr_migratepages = 0;
-			last_migrated_pfn = 0;
 			goto out;
 		case ISOLATE_NONE:
 			if (update_cached) {