Meson8 pwm type always has 4 input clocks. Some inputs may be grounded,
like in the AO domain of some SoCs.

Drop the parent number parameter and make this is constant.
This is also done to make the addition of generic meson8 compatible easier.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20240221151154.26452-4-jbrunet@baylibre.comSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>