net: ag71xx: use ethtool_puts

Allows simplifying get_strings and avoids manual pointer manipulation.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20240905194938.8453-5-rosenp@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>