ARM: dts: qcom: mdm9615: remove invalid spi-max-frequency gsbi3_spi node

The spi-max-frequency property has nothing to do in the controller's node,
remove it and fix the 'spi-max-frequency' was unexpected dtbs check error.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220928-mdm9615-dt-schema-fixes-v4-4-dac2dfaac703@linaro.org