[llvm-mca] remove unused argument from method InstrBuilder::createInstrDescImpl.

We don't need to pass the instruction index to the method that constructs new
instruction descriptors.

No functional change intended.

llvm-svn: 331516
diff --git a/llvm/tools/llvm-mca/Backend.cpp b/llvm/tools/llvm-mca/Backend.cpp
index dbe2012..f000837 100644
--- a/llvm/tools/llvm-mca/Backend.cpp
+++ b/llvm/tools/llvm-mca/Backend.cpp
@@ -33,8 +33,7 @@
 
   while (SM.hasNext()) {
     InstRef IR = SM.peekNext();
-    std::unique_ptr<Instruction> NewIS =
-        IB.createInstruction(IR.first, *IR.second);
+    std::unique_ptr<Instruction> NewIS = IB.createInstruction(*IR.second);
     const InstrDesc &Desc = NewIS->getDesc();
     if (!DU->isAvailable(Desc.NumMicroOps) ||
         !DU->canDispatch(IR.first, *NewIS))