arm64: dts: mediatek: acelink-ew-7886cax: Remove unnecessary cells in spi-nand

There is no need to specify #address-cells and #size-cells in a
node that has only one non-addressable subnode, and this is the
case of the flash@0 node in this devicetree, as it has only one
"partitions" subnode.

Remove those to suppress an avoid_unnecessary_addr_size warning.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Fei Shao <fshao@chromium.org>
Link: https://lore.kernel.org/r/20250724083914.61351-27-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>