ARM: dts: qcom: Use labels with generic node names for ADC channels

A future bindings update will replace the free-form qcom,spmi-vadc and
qcom,spmi-adc5 channel node names with the specific name `channel`, to
be more consistent with how the driver parses the nodes and to match the
generic node name set in `iio/adc/adc.yaml`.

Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20230730-generic-adc-channels-v5-1-e6c69bda8034@somainline.org


Signed-off-by: Bjorn Andersson <andersson@kernel.org>