android : Calculate required KV cache size by summing up tokens size and response token length (#12211)

[hanyin-arm]

Calculate required KV cache size by summing up tokens size and response token length.

previously:
auto n_kv_req = tokens_list.size() + (n_len - tokens_list.size());

now:
auto n_kv_req = tokens_list.size() + n_len;

[ggerganov]

Looks like the n_kv_req is use just to print an error message, so this change should not affect the output of the example.