parisc: led: Fix potential null-ptr-deref in start_task()

start_task() calls create_singlethread_workqueue() and not checked the
ret value, which may return NULL. And a null-ptr-deref may happen:

start_task()
create_singlethread_workqueue() # failed, led_wq is NULL
queue_delayed_work()
queue_delayed_work_on()
__queue_delayed_work() # warning here, but continue
__queue_work() # access wq->flags, null-ptr-deref

Check the ret value and return -ENOMEM if it is NULL.

Fixes: 3499495205a6 ("[PARISC] Use work queue in LED/LCD driver instead of tasklet.")
Signed-off-by: Shang XiaoJing <[e-mail]>
Signed-off-by: Helge Deller <[e-mail]>
Cc: <[e-mail]>

drivers/parisc/led.c

···
 
 	/* Create the work queue and queue the LED task */
 	led_wq = create_singlethread_workqueue("led_wq");	
+	if (!led_wq)
+		return -ENOMEM;
+
 	queue_delayed_work(led_wq, &led_task, 0);
 
 	return 0;