Update missed irc links

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

configure

@@ -534,7 +534,7 @@ die(){
 
 If you think configure made a mistake, make sure you are using the latest
 version from Git.  If the latest version fails, report the problem to the
-ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.freenode.net.
+ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.libera.chat.
 EOF
     if disabled logging; then
         cat <<EOF

doc/writing_filters.txt

@@ -418,4 +418,4 @@ done:
 
 When all of this is done, you can submit your patch to the ffmpeg-devel
 mailing-list for review.  If you need any help, feel free to come on our IRC
-channel, #ffmpeg-devel on irc.freenode.net.
+channel, #ffmpeg-devel on irc.libera.chat.