POSIX: fixed function prototype

Function was changed to be void but prototype was not updated

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/posix/px4_layer/hrt_work.h

@@ -44,7 +44,7 @@ extern struct wqueue_s g_hrt_work;
 
 void hrt_work_queue_init(void);
 int hrt_work_queue(struct work_s *work, worker_t worker, void *arg, uint32_t delay);
-int hrt_work_cancel(struct work_s *work);
+void hrt_work_cancel(struct work_s *work);
 
 inline void hrt_work_lock();
 inline void hrt_work_unlock();