staging: lustre: osc: fix race issues thanks to oap_lock

Fix 'data race condition' defects found by Coverity version 6.5.0:

Data race condition (MISSING_LOCK)

Accessing variable without holding lock. Elsewhere,
this variable is accessed with lock held.

This patch is dedicated to code fragments involving oap_lock.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-2744
Reviewed-on: http://review.whamcloud.com/6572


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