video: s3c-fb: Convert to devm style allocation

Saves some code, especially useful as the code saved is mostly in the
infrequently tested error paths.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>