staging/lustre: update timestamps after buiding rpc

The mtime/atime/ctime in the write RPC has to be updated after
the RPC is built (where xid is generated), otherwise, it could
race with the setattr and updating wrong timestamps on OST side.

Seems this regression was introduced when landing clio code.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-on: http://review.whamcloud.com/13261
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5951


Reviewed-by: John L. Hammond <john.hammond@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>