workqueue: add printf attribute to __alloc_workqueue()

[ Upstream commit d57212f281fda9056412cd6cca983d9d2eb89f53 ]

Fix a compiler warning with W=1:
kernel/workqueue.c: error:
function ‘__alloc_workqueue’ might be a candidate for ‘gnu_printf’
format attribute[-Werror=suggest-attribute=format]
 5657 |  name_len = vsnprintf(wq->name, sizeof(wq->name), fmt, args);
      |  ^~~~~~~~

Fixes: 9b59a85a84 ("workqueue: Don't call va_start / va_end twice")
Signed-off-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

kernel/workqueue.c

@@ -5627,6 +5627,7 @@ static void wq_adjust_max_active(struct workqueue_struct *wq)
 	} while (activated);
 }
 
+__printf(1, 0)
 static struct workqueue_struct *__alloc_workqueue(const char *fmt,
 						  unsigned int flags,
 						  int max_active, va_list args)