dt-bindings: iio: adi,ad74115: remove ref from -nanoamp

dtschema v2023.06 comes with support for properties with -nanoamp
suffix, thus bindings should not have a ref for it:

  adi,ad74115.yaml: properties:adi,ext1-burnout-current-nanoamp: '$ref' should not be valid under {'const': '$ref'}

Cc: Cosmin Tanislav <demonsingur@gmail.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230712080512.94964-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: krzk

Documentation/devicetree/bindings/iio/addac/adi,ad74115.yaml

@@ -216,7 +216,6 @@ properties:
     description: Whether to enable burnout current for EXT1.
 
   adi,ext1-burnout-current-nanoamp:
-    $ref: /schemas/types.yaml#/definitions/uint32
     description:
       Burnout current in nanoamps to be applied to EXT1.
     enum: [0, 50, 500, 1000, 10000]
@@ -233,7 +232,6 @@ properties:
     description: Whether to enable burnout current for EXT2.
 
   adi,ext2-burnout-current-nanoamp:
-    $ref: /schemas/types.yaml#/definitions/uint32
     description: Burnout current in nanoamps to be applied to EXT2.
     enum: [0, 50, 500, 1000, 10000]
     default: 0
@@ -249,7 +247,6 @@ properties:
     description: Whether to enable burnout current for VIOUT.
 
   adi,viout-burnout-current-nanoamp:
-    $ref: /schemas/types.yaml#/definitions/uint32
     description: Burnout current in nanoamps to be applied to VIOUT.
     enum: [0, 1000, 10000]
     default: 0