cluster/afr: Unwind frame on error in readdir[p]

Change-Id: I5701bf115e0aa1adb4fb52f5418534910a2268d4
BUG: 994959
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/5531
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>