ObjPtr<>-ify ClassLinker::FindClass(), fix 1 stale reference use.

Thread::CreateAnnotatedStackTrace() was using a stale
reference `aste_array_class`.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 31113334
Change-Id: I191907c0053456bb57de425aa6ccd9668df818a2
diff --git a/compiler/driver/compiler_driver.cc b/compiler/driver/compiler_driver.cc
index 16f2d0f..653e9ed 100644
--- a/compiler/driver/compiler_driver.cc
+++ b/compiler/driver/compiler_driver.cc
@@ -391,7 +391,7 @@
   DCHECK(driver.GetCompilerOptions().IsQuickeningCompilationEnabled());
   const char* descriptor = dex_file.GetClassDescriptor(class_def);
   ClassLinker* class_linker = runtime->GetClassLinker();
-  mirror::Class* klass = class_linker->FindClass(self, descriptor, class_loader);
+  ObjPtr<mirror::Class> klass = class_linker->FindClass(self, descriptor, class_loader);
   if (klass == nullptr) {
     CHECK(self->IsExceptionPending());
     self->ClearException();