CodeGen: Use MachineInstr& in AntiDepBreaker API, NFC

Take parameters as MachineInstr& instead of MachineInstr* in
AntiDepBreaker API, since these are required to be non-null.  No
functionality change intended.  Looking toward PR26753.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262145 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed