leds-lp55xx: clean up init function

 lp5521/5523_init_device() are replaced with lp55xx common function,
 lp55xx_init_device().

 Error handler in init_device:
 deinit function are matched with 'err_post_init' section in
 lp55xx_init_device().

 Remove LP5523 engine intialization code:
 Engine functionality is not mandatory but optional.
 Moreover engine initialization is done internally with device reset command.
 Therefore, this code is unnecessary.

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