LU-6222 statahead: add to list before make ready

LU-6222 statahead: add to list before make ready

__sa_make_ready() set entry ready before adding to list, so that
revalidate_statahead_dentry()->sa_kill() may free an entry which
is not in any list yet.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: I0b5f7200fb74c88450133d66bf7bf38d9355036f
Reviewed-on: http://review.whamcloud.com/13708
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>