eth: mtk-eth: aarch64: fix build warnings on ethernet-driver

building mtk ethernet driver for aarch64 (mt7622) results
in warnings/errors

  "error: cast from pointer to integer of different size"

Fixes: 23f17164 ("ethernet: MediaTek: add ethernet driver for MediaTek ARM-based SoCs")
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>