leds: convert LM3530 LED driver to devm_kzalloc() and cleanup error exit path

Cc: Shreshtha Kumar SAHU <shreshthakumar.sahu@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>