pwm: meson: remove not needed check in meson_pwm_calc

period >= duty implies that cnt >= duty_cnt. We verified before
that cnt <= 0xffff, therefore we can omit the check here.

Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>