libavformat/libavformat.v: fix application name in comment

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/libavformat.v

 LIBAVFORMAT_$MAJOR {
         global: av*;
-                #FIXME those are for avserver
+                #FIXME those are for ffserver
                 ff_inet_aton;
                 ff_socket_nonblock;
                 ffm_set_write_index;