drm/amdgpu: Skip drm_sched_entity related ops for KIQ ring.

Following change 75fbed20 we never initialize or use the GPU
scheduler for KIQ and hence we need to skip KIQ ring when iterating
amdgpu_ctx's scheduler entites.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>