[ARM] Remove dead assignment.

Found by the Clang static analyzer.

llvm-svn: 224586

llvm/lib/Target/ARM/Thumb1RegisterInfo.cpp

@@ -234,7 +234,6 @@ void llvm::emitThumbRegPlusImmediate(MachineBasicBlock &MBB,
   // If we would emit the copy with an immediate of 0, just use tMOVr.
   if (CopyOpc && Bytes < CopyScale) {
     CopyOpc = ARM::tMOVr;
-    CopyBits = 0;
     CopyScale = 1;
     CopyNeedsCC = false;
     CopyRange = 0;