sched: fix kernel/acct.c comment

fix kernel/acct.c comment.

noticed by Lin Tan. Comment suggested by Olaf Kirch.

also see:

  http://bugzilla.kernel.org/show_bug.cgi?id=8220

Reported-by: tammy000@gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/acct.c b/kernel/acct.c
index fce53d8..cf19547 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -413,7 +413,7 @@
  *  The acct_process() call is the workhorse of the process
  *  accounting system. The struct acct is built here and then written
  *  into the accounting file. This function should only be called from
- *  do_exit().
+ *  do_exit() or when switching to a different output file.
  */
 
 /*