ARM: dts: qcom: align SPMI PMIC ADC node name with dtschema

Bindings expect VADC node name to be "adc":

  pmic@0: 'vadc@3100' does not match any of the regexes

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: David Heidelberg <david@ixit.cz>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220828084341.112146-2-krzysztof.kozlowski@linaro.org