hwmon: (adt7475) Implement support for #pwm-cells = <3>

The adt7475 driver and binding are outliers requiring 4 pwm-cells. The
typical value is 3, there are a few devices that use a lesser value for
historical reasons, no other uses a value bigger than 3.

Implement support for 3 cells to make the adt7475 binding match the
usual PWM binding.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/b5cc994cbe74095e39468fd694c721d7c879db78.1750361514.git.u.kleine-koenig@baylibre.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>