[Flang] Update the fix of PR 80738 to cover generic interface inside modules (#81087)

The following test cases crashes. The problem is that the fix for PR
#80738 is not quite complete.
It should `GetUltimate()` of the `interface_` before check if it is
generic.


```
  MODULE M

    CONTAINS

    FUNCTION Int(Arg)
    INTEGER :: Int, Arg
      Int = Arg
    END FUNCTION

    FUNCTION Int8(Arg)
    INTEGER(8) :: Int8, Arg
      Int8 = 8_8
    END FUNCTION

  END MODULE

  MODULE M1
  USE M

    INTERFACE Int8
      MODULE PROCEDURE  Int
      MODULE PROCEDURE  Int8
    END INTERFACE

  END MODULE

  PROGRAM PtrAssignGen
  USE M
  USE M1
  IMPLICIT NONE

  INTERFACE Int
    MODULE PROCEDURE  Int
    MODULE PROCEDURE  Int8
  END INTERFACE

  PROCEDURE(Int8),   POINTER :: PtrInt8

  PtrInt8 => Int8
  IF ( PtrInt8(100_8) .NE. 8_8 ) ERROR STOP 12

  END
  ```

Author: DanielCChen

flang/lib/Semantics/resolve-names.cpp

@@ -5648,9 +5648,10 @@ void DeclarationVisitor::Post(const parser::ProcDecl &x) {
   const auto &name{std::get<parser::Name>(x.t)};
   const Symbol *procInterface{nullptr};
   if (interfaceName_) {
-    procInterface = interfaceName_->symbol->has<GenericDetails>()
-        ? interfaceName_->symbol->get<GenericDetails>().specific()
-        : interfaceName_->symbol;
+    Symbol *ultimate{&interfaceName_->symbol->GetUltimate()};
+    procInterface = ultimate->has<GenericDetails>()
+        ? ultimate->get<GenericDetails>().specific()
+        : ultimate;
   }
   auto attrs{HandleSaveName(name.source, GetAttrs())};
   DerivedTypeDetails *dtDetails{nullptr};