cluster/dht: Fix unused-but-set-variable warnings

Change-Id: Ie2b2dc54aa0d500c35752c72d3b562bcc05b1fc2
BUG: 969336
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/5123
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>