[llvm] [TTI] Fix haveFastClmul to access inherited DL via thisT() (NFC) (PR #210647)

[Piotr Fusik via llvm-commits]

https://github.com/pfusik commented:

1. What was the error message?

2. If that's an actual bugfix, the commit message shouldn't say "NFC".

3. The surrounding functions use `DL`, `thisT()->getDataLayout()` and `this->getDataLayout()`. Why these differences?

https://github.com/llvm/llvm-project/pull/210647