[Bugfix][Hardware] Fix model input for decode

[yma11]

CPU backend is fixed by #9044 , but I think we can make below changes so that no more fix needed for other backends. Verified on XPU backend.

@LiuXiaoxuanPKU

[github-actions]

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[DarkLight1337]

I prefer fixing the issue on each model runner as IMO passing an empty list instead of None is semantically wrong.

[DarkLight1337]

Not sure what others think?

[jikunshang]

I think this will break multi step features(which num_seqs should be num_steps).
I have a fix here #9145

[njhill]

@DarkLight1337 I agree, it’s potentially more misleading otherwise.

[yma11]

Thanks for everyone's comments. Sorry for not familiar with other path calls about this variable. Let me close it.