arm64: dts: qcom: sm8350: Specify clock-frequency for arch timer

Arch timer runs at 19.2 MHz. Specify the rate in the timer node.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211114012755.112226-4-konrad.dybcio@somainline.org