LU-5837 llite: ll_getparent cleanup

LU-5837 llite: ll_getparent cleanup

Avoid unneeded allocation. Get read-only attributes from the user
getparent structure and write the modified attributes only, instead
of populating a whole structure in kernel and copying it back.

Signed-off-by: Henri Doreau <henri.doreau@cea.fr>
Change-Id: Ifc0632870f80733194384d02d1b4962cdcd75658
Reviewed-on: http://review.whamcloud.com/12527
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: frank zago <fzago@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>