drm/amd/display: Fix Chroma Surface height/width initialization

[why]
Surface height/width for Chroma has another variable that it should be
intialized to, chroma_size. Fixing this will help pass DML2.0 validation
for YCbCr420 tests, DCHB006.109,129, DCHB014.011,012.

[how]
Assign SurfaceHeight/WidthC to chroma_size.height/width

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Sung Joon Kim <sungkim@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>