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/runtime/class_linker-inl.h b/runtime/class_linker-inl.h
index 7a99d3d..25eb85d 100644
--- a/runtime/class_linker-inl.h
+++ b/runtime/class_linker-inl.h
@@ -33,8 +33,8 @@
 
 namespace art {
 
-inline mirror::Class* ClassLinker::FindArrayClass(Thread* self,
-                                                  ObjPtr<mirror::Class>* element_class) {
+inline ObjPtr<mirror::Class> ClassLinker::FindArrayClass(Thread* self,
+                                                         ObjPtr<mirror::Class>* element_class) {
   for (size_t i = 0; i < kFindArrayCacheSize; ++i) {
     // Read the cached array class once to avoid races with other threads setting it.
     ObjPtr<mirror::Class> array_class = find_array_class_cache_[i].Read();