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: NEryu Guan <guaneryu@gmail.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/jbd2/transaction.c

@@ -316,7 +316,8 @@ 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 *jbd2__journal_start(journal_t *journal, int nblocks, int gfp_mask)
 {