drm/amdgpu: remove invalid usage of sched.ready

I can't count how often I had to remove this nonsense.

Probably doesn't need an explanation any more.

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