[flang][OpenMP] Fix the use-associated bug in threadprivate directive lowering

The symbol may be used by use-association for multiple times such
as one in module specification part and one in module procedure.
Then in module procedure, the variable instantiation will be called
for multiple times. But we only need to threadprivatize it once and
use the threadprivatized value for the second time.

Fix #58379.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D136035