net: ethernet: mediatek: remove useless code in mtk_probe()

Remove useless local variables _match_, _soc_ and the code related.

Notice that

const struct of_device_id of_mtk_match[] = {
        { .compatible = "mediatek,mt2701-eth" },
        {},
};

So match->data is NULL.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>