dt-bindings: iio: temperature: ltc2983: change default excitation for custom thermistors

Excitation cannot be set to auto-range when using a custom thermistor
or Steinhart sensor type. Default it to 1000nA to match the driver
and remove the auto-range value from the enum.
Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221103130041.2153295-9-demonsingur@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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

@@ -378,6 +378,11 @@ patternProperties:
             adi,sensor-type:
               const: 26
         then:
+          properties:
+            adi,excitation-current-nanoamp:
+              enum: [250, 500, 1000, 5000, 10000, 25000, 50000, 100000,
+                     250000, 500000, 1000000]
+              default: 1000
           required:
             - adi,custom-steinhart
       - if:
@@ -385,6 +390,11 @@ patternProperties:
             adi,sensor-type:
               const: 27
         then:
+          properties:
+            adi,excitation-current-nanoamp:
+              enum: [250, 500, 1000, 5000, 10000, 25000, 50000, 100000,
+                     250000, 500000, 1000000]
+              default: 1000
           required:
             - adi,custom-thermistor