Use Op<0> accessor instead of OperandList for Instructions.  NFC

This is consistent with other uses of the operand list.  I'm planning a future commit where this will actually matter.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237967 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed