rbd: drop original request earlier for existence check

The reference to the original request dropped at the end of
rbd_img_obj_exists_callback() corresponds to the reference taken
in rbd_img_obj_exists_submit() to account for the stat request
referring to it.  Move the put of that reference up right after
clearing that pointer to make its purpose more obvious.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -2535,6 +2535,7 @@ static void rbd_img_obj_exists_callback(struct rbd_obj_request *obj_request)
 	 */
 	orig_request = obj_request->obj_request;
 	obj_request->obj_request = NULL;
+	rbd_obj_request_put(orig_request);
 	rbd_assert(orig_request);
 	rbd_assert(orig_request->img_request);
 
@@ -2555,7 +2556,6 @@ static void rbd_img_obj_exists_callback(struct rbd_obj_request *obj_request)
 	if (!rbd_dev->parent_overlap) {
 		struct ceph_osd_client *osdc;
 
-		rbd_obj_request_put(orig_request);
 		osdc = &rbd_dev->rbd_client->client->osdc;
 		result = rbd_obj_request_submit(osdc, orig_request);
 		if (!result)
@@ -2585,7 +2585,6 @@ static void rbd_img_obj_exists_callback(struct rbd_obj_request *obj_request)
 out:
 	if (orig_request->result)
 		rbd_obj_request_complete(orig_request);
-	rbd_obj_request_put(orig_request);
 }
 
 static int rbd_img_obj_exists_submit(struct rbd_obj_request *obj_request)