On the XO-1.75, this node represents a bus interface that operates in slave
mode and thus is only able to accommodate a single subnode; no address
cells are necessary.

The Documentation/devicetree/bindings/spi/spi-controller.yaml binding
prefers that we drop the property instead of setting it to zero.

This fixes a DT validation error:

  arch/arm/boot/dts/mmp2-olpc-xo-1-75.dt.yaml: spi@d4037000:
      { ... } is valid under each of {'required': ['spi-slave']},
                                     {'required': ['#address-cells']}

We also need to drop #size-cells:

  arch/arm/boot/dts/mmp2-olpc-xo-1-75.dt.yaml: spi@d4037000:
      '#address-cells' is a dependency of '#size-cells'

Link: https://lore.kernel.org/r/20200718205019.184927-3-lkundrak@v3.skSigned-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>