[PATCH] nbd: fix sparse warning

[Alex Elder <elder@inktank.com>]

I just fixed this in "drivers/block/rbd.c" and I noticed that
"drivers/block/nbd.c" has the same problem.  Fix a warning
issued by sparse by adding some lockdep annotations
to indicate the queue lock gets dropped (because it's
held when do_nbd_request() is called) and re-acquired
within the function.

Signed-off-by: Alex Elder <elder@inktank.com>
---
 drivers/block/nbd.c |    1 +
 1 file changed, 1 insertion(+)

Index: b/drivers/block/nbd.c
===================================================================
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -551,6 +551,7 @@ static int nbd_thread(void *data)
  */

 static void do_nbd_request(struct request_queue *q)
+		__releases(q->queue_lock) __acquires(q->queue_lock)
 {
 	struct request *req;