spi: dt-bindings: spi-controller: explicitly require #address-cells=<0> for slave mode

scripts/dtc/checks.c:
if (get_property(node, "spi-slave"))
	spi_addr_cells = 0;
if (node_addr_cells(node) != spi_addr_cells)
	FAIL(c, dti, node, "incorrect #address-cells for SPI bus");
if (node_size_cells(node) != 0)
	FAIL(c, dti, node, "incorrect #size-cells for SPI bus");

The above code in check_spi_bus_bridge() require that the number of address
cells must be 0. So we should explicitly declare "#address-cells = <0>".

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20201013160845.1772-4-thunder.leizhen@huawei.com


Signed-off-by: Rob Herring <robh@kernel.org>