glusterd: fix compile warning

The following warning has been moved to an error and prevents the smoke tests
in Jenkins to succeed.

  cc1: warnings being treated as errors
  /d/var_lib_jenkins_jobs/smoke/workspace/xlators/mgmt/glusterd/src/glusterd-utils.c: In function ‘glusterd_add_inode_size_to_dict’:
  /d/var_lib_jenkins_jobs/smoke/workspace/xlators/mgmt/glusterd/src/glusterd-utils.c:5038: error: unused variable ‘inode_size’

The warning was introduced with http://review.gluster.org/8491.

Change-Id: I0c824aaf6df70dea35364af6fa72f34eea8c9829
BUG: 1081016
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/8663
Reviewed-by: Santosh Pradhan <spradhan@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>