cluster/afr: remove unused variable

Fix a compiler warning about unused variable. Missed to catch this in
http://review.gluster.org/7723

Change-Id: Iac97051edb97bdd7dbc5f0fd0f2528d4d404d16d
BUG: 1096040
Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-on: http://review.gluster.org/7765
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>