pwm: lpc18xx-sct: Fix a comment to match code

lpc18xx_pwm_probe() only ensures clk_rate <= NSEC_PER_SEC, the following
reasoning is right even under this slightly lesser condition.

Fixes: 8933d30c ("pwm: lpc18xx: Fix period handling")
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Link: https://lore.kernel.org/r/20221108153013.132514-1-u.kleine-koenig@pengutronix.de


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