dt-bindings: iio: Add ltc2983 documentation

Document the LTC2983 temperature sensor devicetree bindings.

Tweaked by Jonathan to take into account the lack of signed output
being maintained by dtc yaml output.  For now a comment added
that the unsigned array should actually be signed.
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -9629,6 +9629,7 @@ W:	http://ez.analog.com/community/linux-device-drivers
 L:	linux-iio@vger.kernel.org
 S:	Supported
 F:	drivers/iio/temperature/ltc2983.c
+F:	Documentation/devicetree/bindings/iio/temperature/adi,ltc2983.yaml
 
 LTC4261 HARDWARE MONITOR DRIVER
 M:	Guenter Roeck <linux@roeck-us.net>