leds-lp55xx: do chip specific configuration on device init

 Chip specific function is configured when the device is initialized.
 So _configure() is moved to each device init function.

 If chip configuration gets failed, the device is de-initialized in
 each _init_device(), not probe().

 For compile error fix, function type declarations are added.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>