lib: media_player: use d3d11drawable vout for callbacks

The d3d11 drawable display doesn't exist yet, but the direct3d11 display
is not reachable from a wextern window (regression from previous commit
e33e383fde that check window type) so we
might as well change it immediately instead of doing it in three steps.

Next commit will re-establish the usage of the display by introducing
it.

lib/media_player.c

@@ -1128,7 +1128,7 @@ bool libvlc_video_set_output_callbacks(libvlc_media_player_t *mp,
     }
     else if ( engine == libvlc_video_engine_d3d11 )
     {
-        var_SetString ( mp, "vout", "direct3d11" );
+        var_SetString ( mp, "vout", "d3d11drawable" );
         var_SetString ( mp, "dec-dev", "d3d11" );
     }
     else if ( engine == libvlc_video_engine_d3d9 )