workqueue: use mod_delayed_work() instead of __cancel + queue

Now that mod_delayed_work() is safe to call from IRQ handlers,
__cancel_delayed_work() followed by queue_delayed_work() can be
replaced with mod_delayed_work().

Most conversions are straight-forward except for the following.

* net/core/link_watch.c: linkwatch_schedule_work() was doing a quite
  elaborate dancing around its delayed_work.  Collapse it such that
  linkwatch_work is queued for immediate execution if LW_URGENT and
  existing timer is kept otherwise.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com> 
diff --git a/drivers/input/mouse/synaptics_i2c.c b/drivers/input/mouse/synaptics_i2c.c
index f1467570..063a174 100644
--- a/drivers/input/mouse/synaptics_i2c.c
+++ b/drivers/input/mouse/synaptics_i2c.c
@@ -376,12 +376,7 @@
 
 	spin_lock_irqsave(&touch->lock, flags);
 
-	/*
-	 * If work is already scheduled then subsequent schedules will not
-	 * change the scheduled time that's why we have to cancel it first.
-	 */
-	__cancel_delayed_work(&touch->dwork);
-	schedule_delayed_work(&touch->dwork, delay);
+	mod_delayed_work(system_wq, &touch->dwork, delay);
 
 	spin_unlock_irqrestore(&touch->lock, flags);
 }