net: igb: convert to timecounter adjtime.

This patch changes the driver to use the new and improved method
for adjusting the offset of a timecounter.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/igb/igb_ptp.c

@@ -256,14 +256,9 @@ static int igb_ptp_adjtime_82576(struct ptp_clock_info *ptp, s64 delta)
 	struct igb_adapter *igb = container_of(ptp, struct igb_adapter,
 					       ptp_caps);
 	unsigned long flags;
-	s64 now;
 
 	spin_lock_irqsave(&igb->tmreg_lock, flags);
-
-	now = timecounter_read(&igb->tc);
-	now += delta;
-	timecounter_init(&igb->tc, &igb->cc, now);
-
+	timecounter_adjtime(&igb->tc, delta);
 	spin_unlock_irqrestore(&igb->tmreg_lock, flags);
 
 	return 0;