drm/amd/amdgpu: Don't proceed in audio_fini if disabled (DCEv10)

If audio is disabled we shouldn't proceed into the fini function.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>