net: ethernet: xscale: Check for PTP support properly

In ixp4xx_get_ts_info() ixp46x_ptp_find() is called
unconditionally despite this feature only existing on
ixp46x, leading to the following splat from tcpdump:

root@OpenWrt:~# tcpdump -vv -X -i eth0
(...)
Unable to handle kernel NULL pointer dereference at virtual address
  00000238 when read
(...)
Call trace:
 ptp_clock_index from ixp46x_ptp_find+0x1c/0x38
 ixp46x_ptp_find from ixp4xx_get_ts_info+0x4c/0x64
 ixp4xx_get_ts_info from __ethtool_get_ts_info+0x90/0x108
 __ethtool_get_ts_info from __dev_ethtool+0xa00/0x2648
 __dev_ethtool from dev_ethtool+0x160/0x234
 dev_ethtool from dev_ioctl+0x2cc/0x460
 dev_ioctl from sock_ioctl+0x1ec/0x524
 sock_ioctl from sys_ioctl+0x51c/0xa94
 sys_ioctl from ret_fast_syscall+0x0/0x44
 (...)
Segmentation fault

Check for ixp46x support before calling PTP.

Fixes: c14e1ec ("net: ixp4xx_eth: convert to ndo_hwtstamp_get() and ndo_hwtstamp_set()")
Signed-off-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: NipaLocal <nipa@local>

Author: linusw

drivers/net/ethernet/xscale/ixp4xx_eth.c

@@ -1014,7 +1014,7 @@ static int ixp4xx_get_ts_info(struct net_device *dev,
 {
 	struct port *port = netdev_priv(dev);
 
-	if (port->phc_index < 0)
+	if (cpu_is_ixp46x() && (port->phc_index < 0))
 		ixp46x_ptp_find(&port->timesync_regs, &port->phc_index);
 
 	info->phc_index = port->phc_index;