[patch 1/1] ixp4xx_eth: fix ptp_ixp46x build failure

When building with ixp4xx_eth and ptp_ixp46x as module, one is getting the
following error:

ERROR: "ixp46x_phc_index" [drivers/ptp/ptp_ixp46x.ko] undefined!

This has been introduced by commit 509a7c25729feab353502e1b544c614772a1d49a.

Signed-off-by: Arnaud Patard <redacted>
Index: efika/drivers/net/ethernet/xscale/ixp4xx_eth.c
===================================================================

--- efika.orig/drivers/net/ethernet/xscale/ixp4xx_eth.c	2012-07-29 14:03:12.710197591 +0200
+++ efika/drivers/net/ethernet/xscale/ixp4xx_eth.c	2012-08-05 11:13:13.188037295 +0200

@@ -1003,6 +1003,7 @@ static int ixp4xx_nway_reset(struct net_
 }
 
 int ixp46x_phc_index = -1;
+EXPORT_SYMBOL_GPL(ixp46x_phc_index);
 
 static int ixp4xx_get_ts_info(struct net_device *dev,
 			      struct ethtool_ts_info *info)