jbd2: Fix comment to match the code in jbd2__journal_start()

jbd2__journal_start() returns an ERR_PTR() value rather than NULL on
failure.

Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 20065c9..9dfdf01 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -316,7 +316,8 @@
  * This function is visible to journal users (like ext3fs), so is not
  * called with the journal already locked.
  *
- * Return a pointer to a newly allocated handle, or NULL on failure
+ * Return a pointer to a newly allocated handle, or an ERR_PTR() value
+ * on failure.
  */
 handle_t *jbd2__journal_start(journal_t *journal, int nblocks, int gfp_mask)
 {