[llvm] [GlobalISel] Fix stale debug location in tryCombineTrunc (PR #216411)

[via llvm-commits]

https://github.com/zhangweize9-cyber commented:

Thank you for your hard work! However, for the maintainability of the submitted source code in the llvm-project community, I'd like to politely ask if you could include a little bit of your own thought process in the description of future pull requests? I understand you've put in a lot of effort, and sharing your thought process to spark friendly discussion within the community will help you quickly improve your skills.

https://github.com/llvm/llvm-project/pull/216411