igb[v],ixgbe: don't use flush_scheduled_work()

All three drivers use flush_scheduled_work() similarly during driver
detach.  Replace it with explicit cancels.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: e1000-devel@lists.sourceforge.net
Cc: netdev@vger.kernel.org
diff --git a/drivers/net/igb/igb_main.c b/drivers/net/igb/igb_main.c
index 041f8e6..62348fc 100644
--- a/drivers/net/igb/igb_main.c
+++ b/drivers/net/igb/igb_main.c
@@ -2050,13 +2050,16 @@
 	struct igb_adapter *adapter = netdev_priv(netdev);
 	struct e1000_hw *hw = &adapter->hw;
 
-	/* flush_scheduled work may reschedule our watchdog task, so
-	 * explicitly disable watchdog tasks from being rescheduled  */
+	/*
+	 * The watchdog timer may be rescheduled, so explicitly
+	 * disable watchdog from being rescheduled.
+	 */
 	set_bit(__IGB_DOWN, &adapter->state);
 	del_timer_sync(&adapter->watchdog_timer);
 	del_timer_sync(&adapter->phy_info_timer);
 
-	flush_scheduled_work();
+	cancel_work_sync(&adapter->reset_task);
+	cancel_work_sync(&adapter->watchdog_task);
 
 #ifdef CONFIG_IGB_DCA
 	if (adapter->flags & IGB_FLAG_DCA_ENABLED) {