staging: lustre: obdclass: simplify cl_lock_fini()

void cl_lock_fini(const struct lu_env *env, struct cl_lock *lock)

{

	cl_lock_trace(D_DLMTRACE, env, "destroy lock", lock);

	while (!list_empty(&lock->cll_layers)) {

	struct cl_lock_slice *slice;

	cl_lock_trace(D_DLMTRACE, env, "destroy lock", lock);

		slice = list_entry(lock->cll_layers.next,

				   struct cl_lock_slice, cls_linkage);

	while ((slice = list_first_entry_or_null(&lock->cll_layers,

						 struct cl_lock_slice,

						 cls_linkage)) != NULL) {

		list_del_init(lock->cll_layers.next);

		slice->cls_ops->clo_fini(env, slice);

	}