net: dsa: realtek: 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/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20231009-strncpy-drivers-net-dsa-realtek-rtl8366-core-c-v1-1-74e1b5190778@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/realtek/rtl8366-core.c

@@ -395,17 +395,13 @@ void rtl8366_get_strings(struct dsa_switch *ds, int port, u32 stringset,
 			 uint8_t *data)
 {
 	struct realtek_priv *priv = ds->priv;
-	struct rtl8366_mib_counter *mib;
 	int i;
 
 	if (port >= priv->num_ports)
 		return;
 
-	for (i = 0; i < priv->num_mib_counters; i++) {
-		mib = &priv->mib_counters[i];
-		strncpy(data + i * ETH_GSTRING_LEN,
-			mib->name, ETH_GSTRING_LEN);
-	}
+	for (i = 0; i < priv->num_mib_counters; i++)
+		ethtool_sprintf(&data, "%s", priv->mib_counters[i].name);
 }
 EXPORT_SYMBOL_GPL(rtl8366_get_strings);