Fix cursorhold_update Configuration Handling in lsp_signature.nvim

[YuCao16]

Hello @ray-x,

I come from Issue #298. I encountered a problem while trying to apply the solution suggested in this issue. Specifically, I found that the configuration option cursorhold_update = false does not work as expected. The root cause appears to be that the autocmd is defined before the user's configuration is applied, resulting in the default settings being used.

Please review the changes and provide feedback. Additionally, it would be great if you could take a look at Issue #298 to confirm if there might be other underlying issues.