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.org


Signed-off-by: Mark Brown <broonie@kernel.org>