LU-13262 ldlm: no current source if lu_ref_del not in same tsk

LU-13262 ldlm: no current source if lu_ref_del not in same tsk

Running with USE_LU_REF ("configure --enable-lu_ref") configured
triggers a LBUG (because "ref->lf_failed > 0" condition false)
due to to using "current" as the lu_ref source, but in some cases
lu_ref_del() occurs within a different task context.
To avoid this, lu_ref source is changed to ldlm_lock address by
this patch.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ia35e31c1a722c03f97672025e2abff40486b3f76
Reviewed-on: https://review.whamcloud.com/37624
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>