Apply clang-tidy fixes for llvm-namespace-comment in OneToNTypeConversion.cpp (NFC)

Author: joker-eph

mlir/lib/Transforms/Utils/OneToNTypeConversion.cpp

@@ -93,7 +93,7 @@ enum class CastKind {
   // cast becomes a target materialization.)
   Target
 };
-}
+} // namespace
 
 /// Mapping of enum values to string values.
 StringRef getCastKindName(CastKind kind) {