igc: Don't reschedule ptp_tx work

The ptp_tx work is scheduled only if TSICR.TXTS bit is set, therefore
TSYNCTXCTL.TXTT_0 bit is expected to be set when we check it igc_ptp_tx_
work(). If it isn't, something is really off and rescheduling the ptp_tx
work to check it later doesn't help much. This patch changes the code to
WARN_ON_ONCE() if this situation ever happens.
Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igc/igc_ptp.c

@@ -429,11 +429,10 @@ static void igc_ptp_tx_work(struct work_struct *work)
 	}
 
 	tsynctxctl = rd32(IGC_TSYNCTXCTL);
-	if (tsynctxctl & IGC_TSYNCTXCTL_TXTT_0)
+	if (WARN_ON_ONCE(!(tsynctxctl & IGC_TSYNCTXCTL_TXTT_0)))
+		return;
+
 	igc_ptp_tx_hwtstamp(adapter);
-	else
-		/* reschedule to check later */
-		schedule_work(&adapter->ptp_tx_work);
 }
 
 /**