pwm: vt8500: Only unprepare the clock after the pwmchip was removed

Until pwmchip_remove() returns the PWM is supposed to work, so
pwmchip_remove() must be called before the clock is stopped.

The return value of pwmchip_remove doesn't need to be checked because
it returns zero anyhow and I plan to make it return void soon.

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