net: phy: tja11xx: 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 dedicated helper function.

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>
Link: https://lore.kernel.org/r/20231012-strncpy-drivers-net-phy-nxp-tja11xx-c-v1-1-5ad6c9dff5c4@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/nxp-tja11xx.c

@@ -414,10 +414,8 @@ static void tja11xx_get_strings(struct phy_device *phydev, u8 *data)
 {
 	int i;
 
-	for (i = 0; i < ARRAY_SIZE(tja11xx_hw_stats); i++) {
-		strncpy(data + i * ETH_GSTRING_LEN,
-			tja11xx_hw_stats[i].string, ETH_GSTRING_LEN);
-	}
+	for (i = 0; i < ARRAY_SIZE(tja11xx_hw_stats); i++)
+		ethtool_sprintf(&data, "%s", tja11xx_hw_stats[i].string);
 }
 
 static void tja11xx_get_stats(struct phy_device *phydev,