[llvm] [memprof] Use a lambda instead of std::bind (NFC) (PR #144940)

[Oliver Stöneberg via llvm-commits]

firewave wrote:

I thought it is just
```cpp
Callback = std::mem_fn(&MemProfReader::idToFrame);
```

But I did not consider that you have to pass the object you are calling on into the call. Sorry for the noise.

https://github.com/llvm/llvm-project/pull/144940