spi-max-frequency is a property of SPI device, not SPI controller.  Drop
it from the controller nodes.  No functional impact expected, although
qcom-msm8960-samsung-expressatt board does not have any child SPI
devices thus the property disappears.  This fixes dtbs_check warnings
like:

  qcom-msm8960-cdp.dtb: spi@16080000: 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/20230619170151.65505-4-krzysztof.kozlowski@linaro.orgSigned-off-by: Bjorn Andersson <andersson@kernel.org>