Don't use UTF16 length as length for MUTF8.

Bug 11367555.

Change-Id: Ia0b07072a1a49d435c3b71ed9a668b316b7ff5d8
diff --git a/compiler/dex/quick/gen_invoke.cc b/compiler/dex/quick/gen_invoke.cc
index 62feade..5a1d3d1 100644
--- a/compiler/dex/quick/gen_invoke.cc
+++ b/compiler/dex/quick/gen_invoke.cc
@@ -1232,7 +1232,7 @@
   const DexFile::MethodId& target_mid = cu_->dex_file->GetMethodId(info->index);
   const DexFile::TypeId& declaring_type = cu_->dex_file->GetTypeId(target_mid.class_idx_);
   StringPiece tgt_methods_declaring_class(
-      cu_->dex_file->StringDataAsStringPieceByIdx(declaring_type.descriptor_idx_));
+      cu_->dex_file->StringDataByIdx(declaring_type.descriptor_idx_));
   if (tgt_methods_declaring_class.starts_with("Ljava/lang/Double;")) {
     std::string tgt_method(PrettyMethod(info->index, *cu_->dex_file));
     if (tgt_method == "long java.lang.Double.doubleToRawLongBits(double)") {