Documentation: fix minor kernel-doc warnings

This patch updates the comments to match the actual code.

Signed-off-by: Martin Waitz <tali@admingilde.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 893d767..6dcce3a 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -258,7 +258,7 @@
 /**
  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
  * @mapping: address_space which was dirtied
- * @nr_pages: number of pages which the caller has just dirtied
+ * @nr_pages_dirtied: number of pages which the caller has just dirtied
  *
  * Processes which are dirtying memory should call in here once for each page
  * which was newly dirtied.  The function will periodically check the system's