net: fec: replace deprecated strncpy with ethtool_sprintf

`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

ethtool_sprintf() is designed specifically for get_strings() usage.
Let's replace strncpy in favor of this more robust and easier to
understand interface.

Also, while we're here, let's change memcpy() over to ethtool_sprintf()
for consistency.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_main.c

@@ -2907,12 +2907,10 @@ static void fec_enet_get_strings(struct net_device *netdev,
 	switch (stringset) {
 	case ETH_SS_STATS:
 		for (i = 0; i < ARRAY_SIZE(fec_stats); i++) {
-			memcpy(data, fec_stats[i].name, ETH_GSTRING_LEN);
-			data += ETH_GSTRING_LEN;
+			ethtool_sprintf(&data, "%s", fec_stats[i].name);
 		}
 		for (i = 0; i < ARRAY_SIZE(fec_xdp_stat_strs); i++) {
-			strncpy(data, fec_xdp_stat_strs[i], ETH_GSTRING_LEN);
-			data += ETH_GSTRING_LEN;
+			ethtool_sprintf(&data, "%s", fec_xdp_stat_strs[i]);
 		}
 		page_pool_ethtool_stats_get_strings(data);