dt-bindings: iio: temperature: ltc2983: Fix child node unevaluated properties

The child node schemas are missing 'unevaluatedProperties' constraints,
so any unknown properties are allowed. The current structure with
multiple patternProperties schemas doesn't work for
unevaluatedProperties as each sub-schema is evaluated independently. To
fix this, move the sub-schema for all child nodes to a $defs entry and
reference it from each named child node.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230404205014.644336-1-robh@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>