drm/amdgpu: Make sure IB tests flushed after IP resume

Fixes: 2c773de2

 (drm/amdgpu: defer test IBs on the rings at boot (V3))

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