llama : fix Gemma-2 Query scaling factors (#8473)

* 9B - query_pre_attn_scalar = 256 not 224

See https://github.com/google/gemma_pytorch/commit/03e657582d17cb5a8617ebf333c1c16f3694670e

Gemma 9b should use 256 and not 224 (self.config.hidden_size // self.config.num_attention_heads)

* llama : fix Gemma-2 Query scaling factor

ggml-ci

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Co-authored-by: Daniel Han <danielhanchen@gmail.com>