leds-lp55xx: clean up init_device() in lp5521/5523

 To make _probe() simple, device initialization code is moved to
 _init_device() at each driver.
 This patch is a preceding step for lp55xx common driver architecture.

 leds-lp5521:
 When 'lp5521_init_device()' gets failed, error handling should be 'fail1'
 rather than 'fail2'.
   fail1: releasing platform resource and return code
   fail2: releasing allocated LED devices with handling 'fail1'
 The 'lp5521_init_device()' is called before creating LED devices.
 Thus, 'goto fail1' is proper error handler of this function.

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