### What this PR does / why we need it?
This PR aims to address the incompatibility of the `.masked_scatter_`
operation in the current `_merge_multimodal_embeddings` function on
Ascend. For now, it reverts to the previous version of the CPU
operation, which can be executed asynchronously on the device side to
enhance performance.
- vLLM version: v0.10.2
- vLLM main:
f225ea7dd9
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Signed-off-by: booker123456 <945658361@qq.com>