[flang] Fix crash from USE-associated defined I/O subprograms

[klausler]

Summary

User-defined derived type I/O implementation subroutines and
generic interfaces may be USE-associated, but the code that builds
the type description table wasn't allowing for that possibility.
Add a call to GetUltimate() to cope.

[PeteSteinfeld]

All builds, tests, and looks good.

flang/lib/Semantics/runtime-type-info.cpp

     GenericKind::DefinedIo definedIo, const Scope *scope) {
   for (; !scope->IsGlobal(); scope = &scope->parent()) {
     if (auto asst{scope->find(name)}; asst != scope->end()) {
-      const Symbol &generic{*asst->second};
+      const Symbol &generic{asst->second->GetUltimate()};
       const auto &genericDetails{generic.get<GenericDetails>()};
       CHECK(std::holds_alternative<GenericKind::DefinedIo>(
           genericDetails.kind().u));