do_invalidatepage() comment typo fix

Fix a typo in the comment for do_invalidatepage().

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
diff --git a/mm/truncate.c b/mm/truncate.c
index cadc156..c3123b0 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -21,7 +21,7 @@
 
 
 /**
- * do_invalidatepage - invalidate part of all of a page
+ * do_invalidatepage - invalidate part or all of a page
  * @page: the page which is affected
  * @offset: the index of the truncation point
  *