drm/amd/display: fix deep color ratio

Fix enum mapping for deep color ratio

Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Hansen Dsouza <Hansen.Dsouza@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>