[ItaniumMangle] Fix a typo.

llvm-svn: 238002
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index f281217..98c38c6 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -221,7 +221,7 @@
   const NamedDecl *Structor;
   unsigned StructorType;
 
-  /// SeqID - The next subsitution sequence number.
+  /// SeqID - The next substitution sequence number.
   unsigned SeqID;
 
   class FunctionTypeDepthState {