net: xgene: fix mdio_np leak in xgene_mdiobus_register()

net: xgene: fix mdio_np leak in xgene_mdiobus_register()

The for_each_child_of_node() loop captures mdio_np via break,
holding the refcount. of_mdiobus_register() does not consume the
reference, so it leaks on success.

Put it after registration.

Fixes: e6ad767305eb ("drivers: net: Add APM X-Gene SoC ethernet driver support.")
Signed-off-by: Shitalkumar Gandhi <shitalkumar.gandhi@cambiumnetworks.com>
Link: https://patch.msgid.link/20260507142024.811543-1-shitalkumar.gandhi@cambiumnetworks.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>