fix compilation

weed/topology/store_replicate.go

@@ -154,8 +154,8 @@ func distributedOperation(locations []operation.Location, store *storage.Store,
 
 func getWritableRemoteReplications(s *storage.Store, volumeId needle.VolumeId, masterNode string) (
 	remoteLocations []operation.Location, err error) {
-	volume := s.GetVolume(volumeId)
-	if volume == nil {
+	v := s.GetVolume(volumeId)
+	if v == nil {
 		return nil, fmt.Errorf("fail to find volume %d", volumeId)
 	}
 	copyCount := v.ReplicaPlacement.GetCopyCount()