[MSAN] clean up style from D131728 - NFC

[kda]

Summary

Depends on D131728

compiler-rt/lib/msan/msan_report.cpp

public:
   Decorator() : SanitizerCommonDecorator() { }
   const char *Origin() const { return Magenta(); }
   const char *Name() const { return Green(); }
 };
 
 static void DescribeStackOrigin(const char *so, uptr pc) {
   Decorator d;
   Printf("%s", d.Origin());
-  if (so == nullptr) {
-    Printf("  %sUninitialized value was created in the stack frame%s\n",
-           d.Origin(), d.Default());
-  } else {
+  if (so) {
     Printf(
         "  %sUninitialized value was created by an allocation of '%s%s%s'"
         " in the stack frame%s\n",
         d.Origin(), d.Name(), so, d.Origin(), d.Default());
+  } else {
+    Printf("  %sUninitialized value was created in the stack frame%s\n",
+           d.Origin(), d.Default());
   }
 
   if (pc)
     StackTrace(&pc, 1).Print();
 }
 
 static void DescribeOrigin(u32 id) {
   VPrintf(1, "  raw origin id: %d\n", id);