block: export blk_get/put_queue for blkback

Impact: build fix

I'm not sure if blkback should be using these functions, but in the
meantime export them to allow blkback to be a module.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

block/blk-core.c

@@ -351,6 +351,7 @@ void blk_put_queue(struct request_queue *q)
 {
 	kobject_put(&q->kobj);
 }
+EXPORT_SYMBOL_GPL(blk_put_queue);
 
 /*
  * Note: If a driver supplied the queue lock, it should not zap that lock
@@ -572,6 +573,7 @@ int blk_get_queue(struct request_queue *q)
 
 	return 1;
 }
+EXPORT_SYMBOL_GPL(blk_get_queue);
 
 static inline void blk_free_request(struct request_queue *q, struct request *rq)
 {