net: ethernet: mtk_eth_soc: fix memory leak in error path

In mtk_ppe_init(), when dmam_alloc_coherent() or devm_kzalloc() failed,
the rhashtable ppe->l2_flows isn't destroyed. Fix it.

In mtk_probe(), when mtk_ppe_init() or mtk_eth_offload_init() or
register_netdev() failed, have the same problem. Fix it.

Fixes: 33fc42de ("net: ethernet: mtk_eth_soc: support creating mac address based offload entries")
Signed-off-by: Yan Cangang <nalanzeyu@gmail.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>