net: dsa: realtek: rtl8365mb: 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: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20231009-strncpy-drivers-net-dsa-realtek-rtl8365mb-c-v1-1-0537fe9fb08c@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/realtek/rtl8365mb.c

@@ -1303,8 +1303,7 @@ static void rtl8365mb_get_strings(struct dsa_switch *ds, int port, u32 stringset
 
 	for (i = 0; i < RTL8365MB_MIB_END; i++) {
 		struct rtl8365mb_mib_counter *mib = &rtl8365mb_mib_counters[i];
-
-		strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTRING_LEN);
+		ethtool_sprintf(&data, "%s", mib->name);
 	}
 }