drm/amdgpu/virtual_dce: drop error message in hw_init

No need to add new asic cases.  This is a sw display
implementation, so just drop the error message so when
we add new asics, all we have to do is add the virtual
dce IP module.

Reviewed-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>