lustre/ptlrpc: rq_commit_cb is called for twice

If a ptlrpc_request is already on imp::imp_replay_list, when it's
replayed and replied, after_reply() will call req::rq_commit_cb
for the request, then call it again in ptlrpc_free_committed.

Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Reviewed-on: http://review.whamcloud.com/8815
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3618


Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>