block/blk-throttle.c: add static to blk_throtl_dispatch_work_fn

blk_throtl_dispatch_work_fn is only used in blk-throttle.c

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-throttle.c

@@ -1258,7 +1258,7 @@ static void throtl_pending_timer_fn(unsigned long arg)
  * of throtl_data->service_queue.  Those bio's are ready and issued by this
  * function.
  */
-void blk_throtl_dispatch_work_fn(struct work_struct *work)
+static void blk_throtl_dispatch_work_fn(struct work_struct *work)
 {
 	struct throtl_data *td = container_of(work, struct throtl_data,
 					      dispatch_work);