arm64: dts: mt8173: elm: Fix nor_flash node property

arm64: dts: mt8173: elm: Fix nor_flash node property

bus-width and non-removable is not used by the driver.
max-frequency should be spi-max-frequency for flash node.

Fixes: 689b937bedde ("arm64: dts: mediatek: add mt8173 elm and hana board")
Reported-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20200727074124.3779237-1-hsinyi@chromium.org
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>