regulator: dt-bindings: pwm-regulator: Add missing type for "pwm-dutycycle-unit"

"pwm-dutycycle-unit" is missing a type, add it.
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Link: https://lore.kernel.org/r/20230613200956.2822740-1-robh@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/pwm-regulator.yaml

@@ -64,6 +64,7 @@ properties:
         defined, <100> is assumed, meaning that
         pwm-dutycycle-range contains values expressed in
         percent.
+    $ref: /schemas/types.yaml#/definitions/uint32
     default: 100
 
   pwm-dutycycle-range: