Eliminate some extraneous code in SlotCalculator::insertVal().

Eliminate some extraneous code in SlotCalculator::insertVal().

Rename SlotCalculator::getValSlot() to SlotCalculator::getSlot(),
       SlotCalculator::insertValue() to SlotCalculator::getOrCreateSlot(),
       SlotCalculator::insertVal() to SlotCalculator::insertValue(), and
       SlotCalculator::doInsertVal() to SlotCalculator::doInsertValue().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@9190 91177308-0d34-0410-b5e6-96231b3b80d8