drm/amdgpu: remove adev and fence from amdgpu_sync_free

Just leftovers from the semaphores.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>