drm/scheduler: change entities rq even earlier

Looks like for correct debugging we need to know the scheduler even
earlier. So move picking a rq for an entity into job creation.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Nayan Deshmukh <nayan26deshmukh@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>