of/address: Constify of_busses[] array and pointers

The of_busses array is fixed, so it and all struct of_bus pointers can
be const.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20241010-dt-const-v1-7-87a51f558425@kernel.org


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