video: s3c-fb: Use s3c_fb_enable() to enable the framebuffer

The s3c-fb driver has a function called s3c_fb_enable() which turns on
and off the physical output. However it is only actually used in paths
which disable the screen, the enabling just writes to the register. Make
the code less confusing by ensuring that the enable also goes through
the same path.

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>