mm/compaction.c: update comment about zone lock in isolate_freepages_block

Since commit f40d1e42 ("mm: compaction: acquire the zone->lock as
late as possible"), isolate_freepages_block() takes the zone->lock
itself.  The function description however still states that the
zone->lock must be held.

This patch removes this outdated statement.
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/compaction.c

@@ -235,10 +235,9 @@ static bool suitable_migration_target(struct page *page)
 }
 
 /*
- * Isolate free pages onto a private freelist. Caller must hold zone->lock.
- * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
- * pages inside of the pageblock (even though it may still end up isolating
- * some pages).
+ * Isolate free pages onto a private freelist. If @strict is true, will abort
+ * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
+ * (even though it may still end up isolating some pages).
  */
 static unsigned long isolate_freepages_block(struct compact_control *cc,
 				unsigned long blockpfn,