ibm_newemac: Fix dangerous struct assumption

The ibm_newemac driver includes code which assumes that the
work_struct which is included in every delayed_work is the first
member of that structure. This is currently the case but might change
in the future, so use to_delayed_work() instead, which doesn't make
such an assumption.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ibm_newemac/core.c

@@ -1229,7 +1229,7 @@ static int emac_link_differs(struct emac_instance *dev)
 static void emac_link_timer(struct work_struct *work)
 {
 	struct emac_instance *dev =
-		container_of((struct delayed_work *)work,
+		container_of(to_delayed_work(work),
 			     struct emac_instance, link_work);
 	int link_poll_interval;