drm/radeon: Use dce5/6 hdmi deep color clock setup also on dce8+

Need to use the adjusted clock on dce8 as well.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=80029



Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>