arm64: dts: qcom: sm8450: drop incorrect cells from serial

The serial/UART device node does not have children with unit addresses,
so address/size cells are not correct.

Fixes: f5837418 ("arm64: dts: qcom: sm8450: add uart20 node")
Fixes: 5188049c ("arm64: dts: qcom: Add base SM8450 DTSI")
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/20230124084951.38195-3-krzysztof.kozlowski@linaro.org