drm/radeon: revert "Prefer lower feedback dividers"

Turns out this breaks a lot of different hardware.

This reverts commit fc8c7052.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>