LU-9210 statahead: missing barrier before wake_up

LU-9210 statahead: missing barrier before wake_up

A barrier is missing before wake_up() in ll_statahead_interpret(),
which may cause 'ls' hang.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Change-Id: I391d6222e353fb27761ffd5412b52ce08f7a0592
Reviewed-on: https://review.whamcloud.com/27330
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>