LU-2101 clio: cl_sync_io_wait() need a barrier

LU-2101 clio: cl_sync_io_wait() need a barrier

cl_sync_io_note() has a small window between cfs_atomic_dec_and_test
and cfs_waitq_broadcast, another thread might have destroyed anchor
between this window, then cl_sync_io_note() is calling wakeup on a
poisoned waitq and crash.

Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Change-Id: I04bfc738c8c5bec3a1e8b51131fae4199ef5ec9a
Reviewed-on: http://review.whamcloud.com/5199
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Hudson
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>