dt-bindings: iio: temperature: ltc2983: describe matrix items

Give a little bit of information on what each item in the matrix is
supposed to be.

Also, some matrices put the 'minItems' and 'maxItems' keywords in the
wrong level. They should be on the same level as the 'items' keyword.
Fix it.

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221103130041.2153295-6-demonsingur@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>