drm/radeon: fix audio dto programming on DCE4+

We need to set the dto source before setting the
dividers otherwise we may get stability problems
with the dto leading to audio playback problems.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: stable@vger.kernel.org