leds-lp5521: clean up lp5521_configure()

leds-lp5521: clean up lp5521_configure()

 This patch is a preceding step for making common lp55xx init function.

 LP5521_REG_R_CURRENT register code moved:
 Chip specific code moved from lp5521_init_device() to lp5521_configure().

 Remove engine init function:
 LP5521 has internal program engines which are used for running LED patterns.
 (blinking, ramp up/down and other emotional visual effects)
 Engine initialization is done by reset command in lp5521_init_device().
 Remove this duplicate code.

 Return code:
 Do not use 'OR' arithmetic for the result.
 If some error occus, just return it.

 Enable latency:
 Use explicit named function, lp5521_wait_enable_done().
 According to the datasheet, 500us is guaranteed time.
 Thus wait time is changed from 1000us to 500us.

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