leds: leds-pca9532 - fix memory leak and properly handle errors

When the registration fails, we need to release the memory we allocated.
Also we need to save the error from led_classdev_register and propagate
it up, else we'll return success, even if we failed.

Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>