ixgbe: don't use magic size number to assign ptp_caps.name

Rather than using a magic size number, just use sizeof since that will
work and is more robust to future changes.
Signed-off-by: NJacob Keller <jacob.e.keller@intel.com>
Tested-by: NPhil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/ixgbe/ixgbe_ptp.c

@@ -840,7 +840,9 @@ void ixgbe_ptp_init(struct ixgbe_adapter *adapter)
 
 	switch (adapter->hw.mac.type) {
 	case ixgbe_mac_X540:
-		snprintf(adapter->ptp_caps.name, 16, "%s", netdev->name);
+		snprintf(adapter->ptp_caps.name,
+			 sizeof(adapter->ptp_caps.name),
+			 "%s", netdev->name);
 		adapter->ptp_caps.owner = THIS_MODULE;
 		adapter->ptp_caps.max_adj = 250000000;
 		adapter->ptp_caps.n_alarm = 0;
@@ -854,7 +856,9 @@ void ixgbe_ptp_init(struct ixgbe_adapter *adapter)
 		adapter->ptp_caps.enable = ixgbe_ptp_enable;
 		break;
 	case ixgbe_mac_82599EB:
-		snprintf(adapter->ptp_caps.name, 16, "%s", netdev->name);
+		snprintf(adapter->ptp_caps.name,
+			 sizeof(adapter->ptp_caps.name),
+			 "%s", netdev->name);
 		adapter->ptp_caps.owner = THIS_MODULE;
 		adapter->ptp_caps.max_adj = 250000000;
 		adapter->ptp_caps.n_alarm = 0;