[NFC][llvm-exegesis] CombinationGenerator::performGeneration(): pull put state...

[NFC][llvm-exegesis] CombinationGenerator::performGeneration(): pull put state increment into lambda

This avoids questionable code such as taking address of current
range-based for variable and comparing it with vector begin iterator.
While this may not be a problem in itself, it can be written more consice.
This was initially suggested by @aaronpuchert.