dt-bindings: iio: dac: adi,ad5758: Drop 'contains' from 'adi,dc-dc-mode'

'contains' applies to arrays, but 'adi,dc-dc-mode' is a scalar. So drop
'contains' from the 'if' schema.
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221111212846.4104059-1-robh@kernel.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/dac/adi,ad5758.yaml

@@ -102,7 +102,6 @@ allOf:
   - if:
       properties:
         adi,dc-dc-mode:
-          contains:
           enum: [1, 3]
     then:
       properties: