[PATCH] trace: add missing forward declaration

[Ahbong Chang]

Without this forward declaration compile may fail if this header is
included only for registering other probe event without struct
pool_workqueue.

Signed-off-by: Ahbong Chang <cwahbong@xxxxxxxxxx>
Reviewed-by: Todd Poynor <toddpoynor@xxxxxxxxxx>
---
 include/trace/events/workqueue.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/trace/events/workqueue.h b/include/trace/events/workqueue.h
index 2f057a494d93..9a761bc6a251 100644
--- a/include/trace/events/workqueue.h
+++ b/include/trace/events/workqueue.h
@@ -25,6 +25,8 @@ DECLARE_EVENT_CLASS(workqueue_work,
 	TP_printk("work struct %p", __entry->work)
 );
 
+struct pool_workqueue;
+
 /**
  * workqueue_queue_work - called when a work gets queued
  * @req_cpu:	the requested cpu
-- 
2.17.0.484.g0c8726318c-goog