pwm: hibvt: Disable the clock only after the PWM was unregistered

The driver is supposed to stay functional until pwmchip_remove()
returns. So disable clocks and reset the hardware only after that.

The return value of pwmchip_remove doesn't need to be checked because
it returns zero anyhow and should be changed to return void eventually.

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