CodeGen: Start removing implicit conversions to/from list iterators, NFC

Start removing implicit conversions to/from list iterators in CodeGen,
ala r249782 for IR.  A lot more to go after this.

llvm-svn: 249851
diff --git a/llvm/lib/CodeGen/ExecutionDepsFix.cpp b/llvm/lib/CodeGen/ExecutionDepsFix.cpp
index 3eee1e2..deacb23 100644
--- a/llvm/lib/CodeGen/ExecutionDepsFix.cpp
+++ b/llvm/lib/CodeGen/ExecutionDepsFix.cpp
@@ -751,7 +751,7 @@
         AliasMap[*AI].push_back(i);
   }
 
-  MachineBasicBlock *Entry = MF->begin();
+  MachineBasicBlock *Entry = &*MF->begin();
   ReversePostOrderTraversal<MachineBasicBlock*> RPOT(Entry);
   SmallVector<MachineBasicBlock*, 16> Loops;
   for (ReversePostOrderTraversal<MachineBasicBlock*>::rpo_iterator