net: cpsw_new: Fix potential unregister of netdev that has not been registered yet

net: cpsw_new: Fix potential unregister of netdev that has not been registered yet

If an error occurs during register_netdev() for the first MAC in
cpsw_register_ports(), even though cpsw->slaves[0].ndev is set to NULL,
cpsw->slaves[1].ndev would remain unchanged. This could later cause
cpsw_unregister_ports() to attempt unregistering the second MAC.
To address this, add a check for ndev->reg_state before calling
unregister_netdev(). With this change, setting cpsw->slaves[i].ndev
to NULL becomes unnecessary and can be removed accordingly.

Fixes: ed3525eda4c4 ("net: ethernet: ti: introduce cpsw switchdev based driver part 1 - dual-emac")
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Link: https://patch.msgid.link/20260205-cpsw-error-path-v1-2-6e58bae6b299@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>