net: dsa: mt7530: 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: Kees Cook <keescook@chromium.org>
Acked-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20231009-strncpy-drivers-net-dsa-mt7530-c-v1-1-ec6677a6436a@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/mt7530.c

@@ -836,8 +836,7 @@ mt7530_get_strings(struct dsa_switch *ds, int port, u32 stringset,
 		return;
 
 	for (i = 0; i < ARRAY_SIZE(mt7530_mib); i++)
-		strncpy(data + i * ETH_GSTRING_LEN, mt7530_mib[i].name,
-			ETH_GSTRING_LEN);
+		ethtool_sprintf(&data, "%s", mt7530_mib[i].name);
 }
 
 static void