video: s3c-fb: s3c_fb_missing_pixclock() can't be __devinit

Since s3c_fb_missing_pixclock() is called from s3c_fb_set_rgb_timing()
which is used in the suspend/resume paths it can't be marked __devinit
as this could result in it being discarded after boot.

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>