net: dsa: lantiq_gswip: 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.

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/90Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20231009-strncpy-drivers-net-dsa-lantiq_gswip-c-v1-1-d55a986a14cc@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/lantiq_gswip.c

@@ -1759,8 +1759,7 @@ static void gswip_get_strings(struct dsa_switch *ds, int port, u32 stringset,
 		return;
 
 	for (i = 0; i < ARRAY_SIZE(gswip_rmon_cnt); i++)
-		strncpy(data + i * ETH_GSTRING_LEN, gswip_rmon_cnt[i].name,
-			ETH_GSTRING_LEN);
+		ethtool_sprintf(&data, "%s", gswip_rmon_cnt[i].name);
 }
 
 static u32 gswip_bcm_ram_entry_read(struct gswip_priv *priv, u32 table,