[rtsan][NFC] Make Uninitialzed state explicit (llvm#109856)

Follow on to llvm#109830 

There should be no functional change, as enums start at 0 anyway. This
just makes the code more readable and prevents any future bugs.

Author: cjappl

compiler-rt/lib/rtsan/rtsan.cpp

@@ -31,7 +31,8 @@ enum class InitializationState : u8 {
 } // namespace
 
 static StaticSpinMutex rtsan_inited_mutex;
-static atomic_uint8_t rtsan_initialized = {0};
+static atomic_uint8_t rtsan_initialized = {
+    static_cast<u8>(InitializationState::Uninitialized)};
 
 static void SetInitializationState(InitializationState state) {
   atomic_store(&rtsan_initialized, static_cast<u8>(state),