spi-max-frequency is a property of SPI device, not SPI controller.  Drop
it from the controller nodes.  No functional impact expected because
child SPI device already defines spi-max-frequency.  This fixes
dtbs_check warnings like:

  qcom-ipq8064-ap148.dtb: spi@1a280000: Unevaluated properties are not allowed ('spi-max-frequency' was unexpected)
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20230619170151.65505-3-krzysztof.kozlowski@linaro.orgSigned-off-by: Bjorn Andersson <andersson@kernel.org>