drm/amd/display: Remove asserts

[why]
Endless assert caused by LinesInDETChroma=0.

[how]
Don't floor for LinesInDETChroma=0

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Jun Lei <jun.lei@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Hong-lu Cheng <hong-lu.cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>