LU-7311 osd: smp_mb__before_clear_bit deprecated since kernel 3.16

LU-7311 osd: smp_mb__before_clear_bit deprecated since kernel 3.16

smp_mb__before_clear_bit() was deprecated in kernel 3.16 and removed
in kernel 3.18, and was replaced by smp_mb__before_atomic(). To fix,
use clear_bit_unlock which does the old smp_mb__before_clear_bit +
clear_bit.

Signed-off-by: frank zago <fzago@cray.com>
Change-Id: I970807ee4c1d91ddda4011ffb22bbe8af0a7764b
Reviewed-on: http://review.whamcloud.com/16891
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>