glusterd: Fixed spurious wakeups in glusterd syncops

glusterd syncops perform a barrier_wake whenever rpc_clnt_submit returned -1.
This is based on the wrong assumption that the cbkfn wasn't called.
This would result in one more wakeup than there ought to be.

BUG: 948686
Change-Id: I839fd218a81255fe50c2047d67461d45360e894d
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4834
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>