staging: lustre: obdclass: optimize busy loop wait

two optimizations in the busy loop wait in class_cleanup():
(1) remove unnecessary spinlocks protecting obd_conn_inprogress
    access
(2) replace cond_resched by more suitable yield to unconditionally
    yield the CPU if the condition check fails.

Signed-off-by: Alexander Zarochentsev <alexander_zarochentsev@xyratex.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5397
Xyratex-bug-id: MRP-1991
Reviewed-on: http://review.whamcloud.com/11198


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>