oledb32: Use an iface instead of a vtbl pointer in IClassFactoryImpl.

dlls/oledb32/main.c

@@ -59,13 +59,18 @@ BOOL WINAPI DllMain(HINSTANCE hinst, DWORD reason, LPVOID lpv)
  */
 typedef struct
 {
-    const IClassFactoryVtbl *lpVtbl;
+    IClassFactory IClassFactory_iface;
     HRESULT (*create_object)( IUnknown*, LPVOID* );
 } cf;
 
+static inline cf *impl_from_IClassFactory(IClassFactory *iface)
+{
+    return CONTAINING_RECORD(iface, cf, IClassFactory_iface);
+}
+
 static HRESULT WINAPI CF_QueryInterface(IClassFactory *iface, REFIID riid, void **obj)
 {
-    cf *This = (cf *)iface;
+    cf *This = impl_from_IClassFactory(iface);
 
     TRACE("(%p, %s, %p)\n", This, debugstr_guid(riid), obj);
 
@@ -91,7 +96,7 @@ static ULONG WINAPI CF_Release(IClassFactory *iface)
 
 static HRESULT WINAPI CF_CreateInstance(IClassFactory *iface, IUnknown *pOuter, REFIID riid, void **obj)
 {
-    cf *This = (cf *)iface;
+    cf *This = impl_from_IClassFactory(iface);
     IUnknown *unk = NULL;
     HRESULT r;
 
@@ -121,7 +126,7 @@ static const IClassFactoryVtbl CF_Vtbl =
     CF_LockServer
 };
 
-static cf oledb_convert_cf = { &CF_Vtbl, create_oledb_convert };
+static cf oledb_convert_cf = { { &CF_Vtbl }, create_oledb_convert };
 
 /******************************************************************
  * DllGetClassObject