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 <[e-mail]>
Reviewed-by: Conor Dooley <[e-mail]>
Reviewed-by: Brian Norris <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

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

···
         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: