leds-lp55xx: use common device attribute driver function
lp5521/5523_register_sysfs() are replaced with lp55xx common driver function,
lp55xx_register_sysfs().
Chip specific device attributes are configurable using 'dev_attr_group'.
Error condition name is changed:
use specific error condition, 'err_register_sysfs' rather than unclear name,
'fail2'.
Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com> Signed-off-by: Bryan Wu <cooloney@gmail.com>