Stop calling ValueObject::SetName from synthetic child providers

Summary:
Calling ValueObject::SetName from a sythetic child provider would change
the underying value object used for the non-synthetic child as well what
is clearly unintentional.

Reviewers: jingham, labath

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D31371

llvm-svn: 299259