[DebugInfo] Follow up to 34cdc91 to fix a crash

We're removing trailing debug-records at the correct time, but from the
wrong block. Broken the iterators buildbot:

  https://lab.llvm.org/buildbot/#/builders/275/builds/1889

Author: jmorse

llvm/lib/IR/BasicBlock.cpp

@@ -1000,7 +1000,7 @@ void BasicBlock::spliceDebugInfoImpl(BasicBlock::iterator Dest, BasicBlock *Src,
     OntoDest->absorbDebugValues(*FromLast, true);
     if (LastIsEnd) {
       FromLast->eraseFromParent();
-      deleteTrailingDPValues();
+      Src->deleteTrailingDPValues();
     }
   }