leds: pca9532: Make pca9532_destroy_devices() return void

Up to now pca9532_destroy_devices() returns always zero because it's
always called with data != NULL. Remove the never-taken error path and
make it return void which makes it easier to see in the callers that
there is no error to handle.

Also the return value of i2c remove callbacks is ignored anyway.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Pavel Machek <pavel@ucw.cz>