llama-quant : correct `n_attention_wv` usage (#20357)

llama-quant : correct `n_attention_wv` usage (#20357)

* llama-quant : correct `n_attention_wv` usage

In #19770, I introduced a regression in the way the
`quantize_state_impl` counter values were initialized. I was
incrementing and using `n_attention_wv` in the same loop, when it should
have been fixed by the time we're deciding tensor types in
`llama_tensor_get_type_impl` (for `use_more_bits`).

I never observed a difference in any of [my
tests](https://github.com/ggml-org/llama.cpp/pull/19770#issuecomment-4000424712)
- it was only after @bartowski kindly pointed this out that I realized
it was incorrect. (Thanks!)

* simplify