pwm: lpc18xx-sct: Free resources only after pwmchip_remove()

Before pwmchip_remove() returns the PWM is expected to be functional. So
remove the pwmchip before disabling the clock.

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