drop more llvm:: prefixes on SmallString<>

More cleanup after r149799.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150380 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/ClangDiagnosticsEmitter.cpp b/utils/TableGen/ClangDiagnosticsEmitter.cpp
index c754ef1..4b041fe 100644
--- a/utils/TableGen/ClangDiagnosticsEmitter.cpp
+++ b/utils/TableGen/ClangDiagnosticsEmitter.cpp
@@ -205,7 +205,7 @@
 static std::string getDiagCategoryEnum(llvm::StringRef name) {
   if (name.empty())
     return "DiagCat_None";
-  llvm::SmallString<256> enumName = llvm::StringRef("DiagCat_");
+  SmallString<256> enumName = llvm::StringRef("DiagCat_");
   for (llvm::StringRef::iterator I = name.begin(), E = name.end(); I != E; ++I)
     enumName += isalnum(*I) ? *I : '_';
   return enumName.str();