nfsd: use to_delayed_work

Use to_delayed_work() instead of open-coding it.
Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -4571,8 +4571,7 @@ static void
 laundromat_main(struct work_struct *laundry)
 {
 	time_t t;
-	struct delayed_work *dwork = container_of(laundry, struct delayed_work,
-						  work);
+	struct delayed_work *dwork = to_delayed_work(laundry);
 	struct nfsd_net *nn = container_of(dwork, struct nfsd_net,
 					   laundromat_work);