CUDA: fix quantized KV cache + multiple sequences (#14822)
* CUDA: fix quantized KV cache + multiple sequences
* Update ggml/src/ggml-cuda/fattn-common.cuh
Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>