staging/lustre/llite: don't d_add for create only files

This is only part of the original Lustre commit. Splitted to remove
d_add() for create only files, because the dentry is fake,
and will be released right after use.

Lustre-change: http://review.whamcloud.com/6797
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3486


Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Peng Tao <bergwolf@gmail.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Alexey Shvetsov <alexxy@gentoo.org>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>