dp83640: Adjust ptp event timestamps

  Event timestamp values should be adjusted by 3*reference clock period +
  11 ns = 35 ns to compensate for input path and synchronization delays.

So subtract 35ns from event timestamps.
Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83640.c

@@ -755,6 +755,9 @@ static int decode_evnt(struct dp83640_private *dp83640,
 	event.type = PTP_CLOCK_EXTTS;
 	event.timestamp = phy2txts(&dp83640->edata);
 
+	/* Compensate for input path and synchronization delays */
+	event.timestamp -= 35;
+
 	for (i = 0; i < N_EXT_TS; i++) {
 		if (ext_status & exts_chan_to_edata(i)) {
 			event.index = i;