e1000e: fix numeric overflow in phc settime method

The PTP Hardware Clock settime function in the e1000e driver
computes nanoseconds from a struct timespec. The code converts the
seconds field .tv_sec by multiplying it with NSEC_PER_SEC. However,
both operands are of type long, resulting in an unintended overflow.
The patch fixes the issue by using the helper function from time.h.

CC: stable <stable@vger.kernel.org>
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/ptp.c

@@ -145,8 +145,7 @@ static int e1000e_phc_settime(struct ptp_clock_info *ptp,
 	unsigned long flags;
 	u64 ns;
 
-	ns = ts->tv_sec * NSEC_PER_SEC;
-	ns += ts->tv_nsec;
+	ns = timespec_to_ns(ts);
 
 	/* reset the timecounter */
 	spin_lock_irqsave(&adapter->systim_lock, flags);