dt-bindings: iio: adc: qcom,spmi-vadc: Allow 1/16 for pre-scaling

The channel ADC5_USB_IN_V_16 is using 1/16 pre-scaling on at least
pm7250b and pmi632. Allow that in the schema.

Signed-off-by: Luca Weiss <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/adc/qcom,spmi-vadc.yaml

···
         oneOf:
           - items:
               - const: 1
-              - enum: [ 1, 3, 4, 6, 20, 8, 10 ]
+              - enum: [ 1, 3, 4, 6, 20, 8, 10, 16 ]
           - items:
               - const: 10
               - const: 81