LU-5409 mdd: use DT wrappers

LU-5409 mdd: use DT wrappers

In lustre/mdd replace direct calls to members of dt_object_operations
with calls to the equivalent static inline functions.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Iaf21970e582f30f903e07615c59c306f413d16dc
Reviewed-on: http://review.whamcloud.com/11264
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>