libglusterfs: Fix unused variable warning

Change-Id: If385ba0993fdbd3e3b7500b2b6631721911e0ab3
BUG: 1100144
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/7858
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>