leds: an30259a: add a check for devm_regmap_init_i2c

an30259a_probe misses a check for devm_regmap_init_i2c and may cause
problems.
Add a check and print errors like other leds drivers.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>