debug/io-stats: Free conf on init failures

Change-Id: I1d227f7b2b8f8ad8d44df8711654ee885e79cf38
BUG: 1111557
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/8148
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>