jbd: Fix comment to match the code in journal_start()

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

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/jbd/transaction.c

@@ -266,7 +266,8 @@ static handle_t *new_handle(int nblocks)
  * 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 *journal_start(journal_t *journal, int nblocks)
 {