net: ag71xx: get reset control using devm api

Currently, the of variant is missing reset_control_put in error paths.
The devm variant does not require it.

Allows removing mdio_reset from the struct as it is not used outside the
function.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20240905194938.8453-6-rosenp@gmail.com


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