ART: Fix uninitialized value in arm32 assembler test

The first_ field was meant to be initialized for each generation
invocation.

Change-Id: If4d36d84afe24d8ddc6bb9d25b85c764285e166a
diff --git a/compiler/utils/arm/assembler_arm32_test.cc b/compiler/utils/arm/assembler_arm32_test.cc
index 30b89e1..837fe1e 100644
--- a/compiler/utils/arm/assembler_arm32_test.cc
+++ b/compiler/utils/arm/assembler_arm32_test.cc
@@ -421,6 +421,7 @@
   template <typename... Args>
   void GenericTemplateHelper(std::function<void(Args...)> f, bool without_pc,
                              std::string fmt, std::string test_name) {
+    first_ = false;
     WarnOnCombinations(CountHelper<Args...>(without_pc));
 
     std::ostringstream oss;