croppadd: use correct shortname 'croppadd'

The shortname was 'cropadd' while the module was compiled as 'croppadd' (notice the extra 'p').
The module was correctly build, but was not loadable

modules/video_filter/croppadd.c

@@ -75,7 +75,7 @@ static picture_t *Filter( filter_t *, picture_t * );
  * Module descriptor
  *****************************************************************************/
 vlc_module_begin ()
-    set_shortname( N_("Cropadd") )
+    set_shortname( N_("Croppadd") )
     set_description( N_("Video cropping filter") )
     set_capability( "video filter2", 0 )
     set_callbacks( OpenFilter, CloseFilter )