Fix a warning about named return value not being moved-from.

The use of an rvalue reference here was using reference lifetime
extension needlessly - the code is simpler and more efficient without
it.

lldb/source/Interpreter/OptionValue.cpp

@@ -569,7 +569,7 @@ bool OptionValue::DumpQualifiedName(Stream &strm) const {
 }
 
 OptionValueSP OptionValue::DeepCopy(const OptionValueSP &new_parent) const {
-  auto &&clone = Clone();
+  auto clone = Clone();
   clone->SetParent(new_parent);
   return clone;
 }