usb: phy: mv-otg: use to_delayed_work instead of cast

Directly casting a work_struct pointer to a delayed_work is risky if the
work member of struct delayed_work is ever moved from being the first
member.

Instead, use the inline function to_delayed_work(), which does the same
cast in a safer way (using container_of).
Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/otg/mv_otg.c

@@ -420,7 +420,7 @@ static void mv_otg_work(struct work_struct *work)
 	struct usb_otg *otg;
 	int old_state;
 
-	mvotg = container_of((struct delayed_work *)work, struct mv_otg, work);
+	mvotg = container_of(to_delayed_work(work), struct mv_otg, work);
 
 run:
 	/* work queue is single thread, or we need spin_lock to protect */