[flang] preserve symbol in DescriptorInquiry

Do not use ultimate symbols in DescriptorInquiry. Using the ultimate
symbol may lead to issues later for at least two reasons:

- The original symbols may have volatile/asynchronous attributes that
  the ultimate may not have. Later phases working on the DescriptorInquiry
  would then not apply potential care required by these attributes.
- HostAssociatedDetails symbols are used by OpenMP for symbols with
  special OpenMP attributes inside OpenMP region (e.g variables with
  private attribute), so it is very important to preserve this
  aspect in the DescriptorInquiry, that would otherwise apply on the
  symbol outside of the region.

Differential Revision: https://reviews.llvm.org/D104385