tiling: Fix "maximize" tile with no chrome at the top

The original patch triggered "maximize" when the window was dragged
to the top, so that the pointer was below or on the monitor edge and
above the work area's top.

If there's no chrome at the top of the monitor, so that monitor edge
and work area top fall together, the pointer cannot be moved above
the work area's top, so tiling was not triggered.

src/core/window.c

@@ -7861,7 +7861,7 @@ update_move (MetaWindow  *window,
               x < (monitor->rect.x + monitor->rect.width))
             {
               /* check if cursor is on the top edge of the monitor*/
-              if (y >= monitor->rect.y && y < work_area.y)
+              if (y >= monitor->rect.y && y <= work_area.y)
                   window->tile_mode = META_TILE_MAXIMIZED;
             }
         }