i40e: only warn once of PTP nonsupport in 100Mbit speed

Only warn once that PTP is not supported when linked at 100Mbit.

Yes, using a static this way means that this once-only message is not
port specific, but once only for the life of the driver, regardless of
the number of ports.  That should be plenty.

Change-ID: Ie6476530056df408452e195ef06afd4f57caa4b2
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_ptp.c

@@ -382,11 +382,17 @@ void i40e_ptp_set_increment(struct i40e_pf *pf)
 		incval = I40E_PTP_1GB_INCVAL;
 		break;
 	case I40E_LINK_SPEED_100MB:
-		dev_warn(&pf->pdev->dev,
-			 "%s: 1588 functionality is not supported at 100 Mbps. Stopping the PHC.\n",
-			 __func__);
+	{
+		static int warn_once;
+
+		if (!warn_once) {
+			dev_warn(&pf->pdev->dev,
+				 "1588 functionality is not supported at 100 Mbps. Stopping the PHC.\n");
+			warn_once++;
+		}
 		incval = 0;
 		break;
+	}
 	case I40E_LINK_SPEED_40GB:
 	default:
 		incval = I40E_PTP_40GB_INCVAL;