drm/amd/display: fix use of uninitialized memory

DML does not calculate chroma values for RQ when surface is not YUV, but DC
will unconditionally use the uninitialized values for HW programming.
This does not cause visual corruption since HW will ignore garbage chroma
values when surface is not YUV, but causes presubmission tests to fail
golden value comparison.

Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Signed-off-by: Eryk Brol <eryk.brol@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>