leds: Convert S3C24XX LED driver to devm_kzalloc()

Use the device managed resource API for simplifying
the error/driver remove paths.

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>