dt-bindings: misc: explicitly add #address-cells for slave mode

dt-bindings: misc: explicitly add #address-cells for slave mode

Explicitly add "#address-cells = <0>" and "#size-cells = <0>" to
eliminate below warnings.

(spi_bus_bridge): /example-0/spi: incorrect #address-cells for SPI bus
(spi_bus_bridge): /example-0/spi: incorrect #size-cells for SPI bus
(spi_bus_reg): Failed prerequisite 'spi_bus_bridge'

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20201013160845.1772-5-thunder.leizhen@huawei.com
Signed-off-by: Rob Herring <robh@kernel.org>