Avoid creating tensor in CosmosAttnProcessor2_0 (#11761)

[chenxiao111222]

What does this PR do?

Fixes #11761

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[a-r-r-o-w]

Just wanted to make a note that the reason this has to be a tensor is because it seemingly breaks ONNX export. I had it implemented the same way earlier but changed to this after suggestions from the nvidia team. cc @asfiyab-nvidia