[llvm-mca] Fix class dominance warnings for parseCodeRegions

Fixes issue [59091](https://github.com/llvm/llvm-project/issues/59091).

`CodeRegionGenerator::parseCodeRegions` is implemented by `AsmCodeRegionGenerator`.
If it were to be implemented in `AnalysisRegionGenerator` or `InstrumentRegionGenerator`,
then `parseCodeRegions` from an `AsmAnalysisRegionGenerator` or `AsmInstrumentRegionGenerator`
object would be ambiguous. To solve this, `AsmAnalysisRegionGenerator` and
`AsmInstrumentRegionGenerator` qualify their call to `AsmCodeRegionGenerator::parseCodeRegions`.

Differential Revision: https://reviews.llvm.org/D138462