drivers: leds: tlc591xx: check error during device init

The driver currently ignores errors from register writes at probe time.
It will hence register an LED class device no matter whether the
pyhsical device is present or not.

To fix this, make the device probe fail in case regmap operations
return an error.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>