CalcSpillWeights: give a better describing name to calculateSpillWeights

Besides, this relates it more obviously to the VirtRegAuxInfo::calculateSpillWeightAndHint.

No functionnal change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194404 91177308-0d34-0410-b5e6-96231b3b80d8