leds-lp55xx: use lp55xx common deinit function

 Two separate de-init functions are merged into one common function.
 And it is used in err_post_init of lp55xx_init_device().

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