staging: greybus: pwm: Rely on pwm framework to pass a valid hwpwm

The pwm framework already asserts to only pass a hwpwm value (= which)
less than npwm (= pwmc->pwm_max + 1). So there is no need to recheck
this condition. Drop the respective checks.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/e003bc5e8e66f27f2b8fdc525a536d865888cffe.1707900770.git.u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>