Fix bogus AbortIfNotZeroExtended on x64 for bounds checks

R=mmassi@chromium.org

Review URL: https://chromiumcodereview.appspot.com/10837019

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12234 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/lithium-codegen-x64.cc

@@ -3623,7 +3623,7 @@ void LCodeGen::DoBoundsCheck(LBoundsCheck* instr) {
   if (instr->length()->IsRegister()) {
     Register reg = ToRegister(instr->length());
     if (FLAG_debug_code &&
-        !instr->hydrogen()->index()->representation().IsTagged()) {
+        !instr->hydrogen()->length()->representation().IsTagged()) {
       __ AbortIfNotZeroExtended(reg);
     }
     if (instr->index()->IsConstantOperand()) {