msm: vdec: Avoid setting incorrect color format for DPB buffers

When decoder output buffers get split due to color
format, the color format for DPB buffers was wrongly
set. Color format for OPB buffers was set for DPB as
well. This led to color distortion while decoding
cetain contents in split mode.
The code change avoids overwriting the improper color
format for DPB buffers which was earlier set correctly
while deciding the split mode.

Change-Id: I71924f370c92c7875706c350f74c7859852c4809
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>