net: dsa: lan9303: use ethtool_puts() for lan9303_get_strings()

net: dsa: lan9303: use ethtool_puts() for lan9303_get_strings()

This pattern of strncpy with some pointer arithmetic setting fixed-sized
intervals with string literal data is a bit weird so let's use
ethtool_puts() as this has more obvious behavior and is less-error
prone.

Nicely, we also get to drop a usage of the now deprecated strncpy() [1].

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://github.com/KSPP/linux/issues/90
Suggested-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20240425-strncpy-drivers-net-dsa-lan9303-core-c-v4-1-9fafd419d7bb@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>