arm64: dts: qcom: ipq6018-cp01-c1: drop SPI cs-select

The SPI controller nodes do not use/allow cs-select property:

  ipq6018-cp01-c1.dtb: spi@78b5000: Unevaluated properties are not allowed ('cs-select' was unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230308125906.236885-6-krzysztof.kozlowski@linaro.org