Call the correct destructor.

llvm-svn: 51544
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 7c44a20c..a9afc81 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -231,7 +231,7 @@
   // NamespaceDecl uses "NextDeclarator" to chain namespace declarations
   // together. They are all top-level Decls.
   
-  this->~Decl();
+  this->~NamespaceDecl();
   C.getAllocator().Deallocate((void *)this);
 }