workqueue: fix a kernel-doc warning

As warned by Sphinx:

	./Documentation/core-api/workqueue:400: ./kernel/workqueue.c:1218: WARNING: Unexpected indentation.

the return code table is currently not recognized, as it lacks
markups.
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

kernel/workqueue.c

@@ -1212,11 +1212,14 @@ static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, int color)
  * stable state - idle, on timer or on worklist.
  *
  * Return:
+ *
+ *  ========	================================================================
  *  1		if @work was pending and we successfully stole PENDING
  *  0		if @work was idle and we claimed PENDING
  *  -EAGAIN	if PENDING couldn't be grabbed at the moment, safe to busy-retry
  *  -ENOENT	if someone else is canceling @work, this state may persist
  *		for arbitrarily long
+ *  ========	================================================================
  *
  * Note:
  * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting