cluster/afr: Fix a minor typo.

Change-Id: I2e1bb21febb6754ed8772df6342c5c06aac95046
BUG: 1133949
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/8545
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>