zoltan: Minor change addressing #4032

Created by: kddevin

@trilinos/zoltan

Description

Minor change meant to remove compiler warnings described in #4032 (closed)

Motivation and Context

Build without warnings

How Has This Been Tested?

Built/run on linux workstation. I was unable to reproduce warnings using gcc 7.2, so I do not know that this change will remove them. This change was recommended by @mhoemmen