dt-bindings: iio: temperature: ltc2983: describe broken mux delay property

The 'adi,mux-delay-config-us' property is broken. It was supposed to
be in us, but the value is actually written directly to the register.
Describe the fact that it is broken and how it actually works.
Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221103130041.2153295-11-demonsingur@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/temperature/adi,ltc2983.yaml

@@ -29,6 +29,9 @@ properties:
       Extra delay prior to each conversion, in addition to the internal 1ms
       delay, for the multiplexer to switch input configurations and
       excitation values.
+
+      This property is supposed to be in microseconds, but to maintain
+      compatibility, this value will be multiplied by 100 before usage.
     maximum: 255
     default: 0