arm64: dts: qcom: pm8998: Add die temperature channel node to the ADC

Add a channel node for the die temperature to the ADC.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>