widl: Fix a typo when removing TYPEFLAG_FDUAL.

tools/widl/write_msft.c

diff --git a/tools/widl/write_msft.c b/tools/widl/write_msft.c
index 725b361..ffbe9f8 100644
--- a/tools/widl/write_msft.c
+++ b/tools/widl/write_msft.c
@@ -1877,7 +1877,7 @@
 
     /* can't be dual if it doesn't derive from IDispatch */
     if (!(msft_typeinfo->typeinfo->flags & 0x1000)) /* TYPEFLAG_FDISPATCHABLE */
-        msft_typeinfo->typeinfo->flags &= 0x40; /* TYPEFLAG_FDUAL */
+        msft_typeinfo->typeinfo->flags &= ~0x40; /* TYPEFLAG_FDUAL */
 
     if(interface->ref)
         add_impl_type(msft_typeinfo, interface->ref);