[LLDB] Fix how ValueObjectChild handles bit-fields stored in a Scalar in UpdateValue()

When bit-field data was stored in a Scalar in ValueObjectChild during UpdateValue()
it was extracting the bit-field value. Later on in lldb_private::DumpDataExtractor(…)
we were again attempting to extract the bit-field. Which would then not obtain the
correct value. This will remove the extra extraction in UpdateValue().
We hit this specific case when values are passed in registers, which we could only
reproduce in an optimized build.

Differential Revision: https://reviews.llvm.org/D85376