mlang: Return S_OK from fnIMultiLanguage2_SetMimeDBSource.

The source is largely irrelevant since we are not likely to be wanting
to ship updates to the MIME database as registry updates, instead of
just changing the code.
diff --git a/dlls/mlang/mlang.c b/dlls/mlang/mlang.c
index 1dfb9fc..835a7b3 100644
--- a/dlls/mlang/mlang.c
+++ b/dlls/mlang/mlang.c
@@ -2228,8 +2228,8 @@
     IMultiLanguage2* iface,
     MIMECONTF dwSource)
 {
-    FIXME("\n");
-    return E_NOTIMPL;
+    FIXME("0x%08x\n", dwSource);
+    return S_OK;
 }
 
 static HRESULT WINAPI fnIMultiLanguage2_GetNumberOfScripts(