wmiutils: Use an iface instead of a vtbl pointer in wmiutils_cf.

dlls/wmiutils/main.c

@@ -39,13 +39,13 @@ typedef HRESULT (*fnCreateInstance)( IUnknown *pUnkOuter, LPVOID *ppObj );
 
 typedef struct
 {
-    const struct IClassFactoryVtbl *vtbl;
+    IClassFactory IClassFactory_iface;
     fnCreateInstance pfnCreateInstance;
 } wmiutils_cf;
 
 static inline wmiutils_cf *impl_from_IClassFactory( IClassFactory *iface )
 {
-    return (wmiutils_cf *)((char *)iface - FIELD_OFFSET( wmiutils_cf, vtbl ));
+    return CONTAINING_RECORD(iface, wmiutils_cf, IClassFactory_iface);
 }
 
 static HRESULT WINAPI wmiutils_cf_QueryInterface( IClassFactory *iface, REFIID riid, LPVOID *ppobj )
@@ -112,7 +112,7 @@ static const struct IClassFactoryVtbl wmiutils_cf_vtbl =
     wmiutils_cf_LockServer
 };
 
-static wmiutils_cf status_code_cf = { &wmiutils_cf_vtbl, WbemStatusCodeText_create };
+static wmiutils_cf status_code_cf = { { &wmiutils_cf_vtbl }, WbemStatusCodeText_create };
 
 BOOL WINAPI DllMain( HINSTANCE hinst, DWORD reason, LPVOID lpv )
 {
@@ -138,7 +138,7 @@ HRESULT WINAPI DllGetClassObject( REFCLSID rclsid, REFIID iid, LPVOID *ppv )
 
     if (IsEqualGUID( rclsid, &CLSID_WbemStatusCode ))
     {
-       cf = (IClassFactory *)&status_code_cf.vtbl;
+       cf = &status_code_cf.IClassFactory_iface;
     }
     if (!cf) return CLASS_E_CLASSNOTAVAILABLE;
     return IClassFactory_QueryInterface( cf, iid, ppv );