igb: re-use igb_ptp_reset in igb_ptp_init

Modify igb_ptp_init to take advantage of igb_ptp_reset, and remove
duplicated work that was occurring in both igb_ptp_reset and
igb_ptp_init.

In total, resetting the TSAUXC register, and resetting the system time
both happen in igb_ptp_reset already. igb_ptp_reset now also takes care
of starting the delayed work item for overflow checks, as well.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index ef3d642..750a5d8 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -2027,7 +2027,8 @@
 	wr32(E1000_VET, ETHERNET_IEEE_VLAN_TYPE);
 
 	/* Re-enable PTP, where applicable. */
-	igb_ptp_reset(adapter);
+	if (adapter->ptp_flags & IGB_PTP_ENABLED)
+		igb_ptp_reset(adapter);
 
 	igb_get_phy_info(hw);
 }