leds-lp55xx: use lp55xx common init function - post int

 LP5521/5523 chip configuration is replaced with lp55xx common function,
 lp55xx_post_init_device().

 Name change:
 lp5521/5523_configure() to lp5521/5523_post_init_device()
 These are called in init function.

 Register access function
 Argument type is changed from 'i2c_client' to 'lp55xx_chip'.
 Use exported R/W functions of lp55xx common driver.

 Temporary variables in lp5521/5523_init_device()
 These functions will be removed but temporary variables are needed for
 blocking build warnings - incompatible pointer.

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