igb: Fix sparse warning in igb_ptp_rx_pktstamp

This change fixes a sparse warning triggered by us casting the timestamp in
the packet as a u64 instead of as a __le64.  This change corrects that in
order to resolve the sparse warning.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_ptp.c

@@ -455,7 +455,7 @@ void igb_ptp_rx_pktstamp(struct igb_q_vector *q_vector,
 			 unsigned char *va,
 			 struct sk_buff *skb)
 {
-	u64 *regval = (u64 *)va;
+	__le64 *regval = (__le64 *)va;
 
 	/*
 	 * The timestamp is recorded in little endian format.