FreeBSD: Sync taskq_cancel_id() returns with Linux

Couple places in the code depend on 0 returned only if the task was
actually cancelled.  Doing otherwise could lead to extra references
being dropped.  The race could be small, but I believe CI hit it
from time to time.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes openzfs#16565

module/os/freebsd/spl/spl_taskq.c

@@ -357,7 +357,7 @@ taskq_cancel_id(taskq_t *tq, taskqid_t tid)
 	taskq_ent_t *ent;
 
 	if ((ent = taskq_lookup(tid)) == NULL)
-		return (0);
+		return (ENOENT);
 
 	if (ent->tqent_type == NORMAL_TASK) {
 		rc = taskqueue_cancel(tq->tq_queue, &ent->tqent_task, &pend);
@@ -380,7 +380,7 @@ taskq_cancel_id(taskq_t *tq, taskqid_t tid)
 	}
 	/* Free the extra reference we added with taskq_lookup. */
 	taskq_free(ent);
-	return (rc);
+	return (pend ? 0 : ENOENT);
 }
 
 static void