Add 'void' keyword to parameterless function declaration.

Originally committed as revision 16861 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffserver.c

@@ -4441,7 +4441,7 @@ static void handle_child_exit(int sig)
     need_to_start_children = 1;
 }
 
-static void opt_debug()
+static void opt_debug(void)
 {
     ffserver_debug = 1;
     ffserver_daemon = 0;