video: s3c-fb: correct transparency checking in 32bpp

32bpp means ARGB 8888 in the driver, therfore the transparency length
and offset should be 8 and 24 respectively. However, the transparency
length and offset were previously 0, which means that the driver supports
RGB 888 without alpha blending when 32bpp is used.

So, the transparency checking in 32bpp is corrected so that the
transparency length and offset are 8 and 24 respectively.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>