Fix asan error in stack usage (#6434)

* Incorrectly used a reference to the popped top of stack

See google internal bug: b/462029612

source/val/validate_logical_pointers.cpp

diff --git a/source/val/validate_logical_pointers.cpp b/source/val/validate_logical_pointers.cpp
index 1528701..8ad3e6d 100644
--- a/source/val/validate_logical_pointers.cpp
+++ b/source/val/validate_logical_pointers.cpp
@@ -625,7 +625,7 @@
               trace_inst->uses());
           std::unordered_set<const Instruction*> store_seen;
           while (!store_stack.empty()) {
-            const auto& use = store_stack.back();
+            const auto use = store_stack.back();
             store_stack.pop_back();
 
             if (!store_seen.insert(use.first).second) {
@@ -766,7 +766,7 @@
               trace_inst->uses());
           std::unordered_set<const Instruction*> store_seen;
           while (!store_stack.empty()) {
-            const auto& use = store_stack.back();
+            const auto use = store_stack.back();
             store_stack.pop_back();
 
             if (!store_seen.insert(use.first).second) {