glusterd: remove extra call to glusterd_volume_compute_cksum()

In the commit phase of volume create, checksum on volinfo is
computed twice - once in the call to glusterd_store_volinfo() and once,
further down, in the same function glusterd_op_create_volume().

Change-Id: I36f9426943cd48937d4946b4b4ef09f19f31d888
BUG: 812356
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: http://review.gluster.org/4463
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>