[PyTorch] Remove unnecessary shared_ptr copies in ThreadLocalDebugInf…

…o::get (#47791)

Summary:
Pull Request resolved: #47791

`debug_info` is `thread_local` and this function is a leaf, so nobody else could free it out from under us. Regular pointer should be fine.
ghstack-source-id: 116456975

Test Plan: Run framework overhead benchmarks

Reviewed By: bhosmer

Differential Revision: D24901749

fbshipit-source-id: c01a60b609fd08e5200264d8e98d356e2c78cf28

c10/util/ThreadLocalDebugInfo.cpp

@@ -9,12 +9,12 @@ thread_local std::shared_ptr<ThreadLocalDebugInfo> debug_info = nullptr;
 /* static */
 std::shared_ptr<DebugInfoBase> ThreadLocalDebugInfo::get(
     DebugInfoKind kind) {
-  auto cur = debug_info;
+  ThreadLocalDebugInfo* cur = debug_info.get();
   while (cur) {
     if (cur->kind_ == kind) {
       return cur->info_;
     }
-    cur = cur->parent_info_;
+    cur = cur->parent_info_.get();
   }
   return nullptr;
 }