mm: compaction: make compact_zone_order() static

There's no compact_zone_order() user outside file scope, so make it static.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/compaction.c b/mm/compaction.c
index a0e4202..899d956 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -582,7 +582,7 @@
 	return ret;
 }
 
-unsigned long compact_zone_order(struct zone *zone,
+static unsigned long compact_zone_order(struct zone *zone,
 				 int order, gfp_t gfp_mask,
 				 bool sync)
 {