fix --use-cpu-initialization error when expert is not tensor-parallel

[taozhiwei]

Use --use-cpu-initialization will be failed When non-expert is tensor-parallel and expert is not tensor-parallel.
because per_partition_size is equal to master_weight.shape[partition_dim], so my_weight_list len is 0 except in 0 rank , so we can not use torch.cat, We should use assign.
Please help review @GuanhuaWang @tjruwase, thanks.