Fix sizeof mismatch (cid #1049614)

modules/demux/mkv/mkv.cpp

@@ -301,7 +301,7 @@ static int Control( demux_t *p_demux, int i_query, va_list args )
                 return VLC_EGENERIC;
 
             *pi_int = p_sys->stored_attachments.size();
-            *ppp_attach = (input_attachment_t**)malloc( sizeof(input_attachment_t**) *
+            *ppp_attach = (input_attachment_t**)malloc( sizeof(input_attachment_t*) *
                                                         p_sys->stored_attachments.size() );
             if( !(*ppp_attach) )
                 return VLC_ENOMEM;