cmdutils: fix new API break the "ffmpeg -muxers/demuxers"

fix commit 22381906 break the "ffmpeg -muxers/demuxers".
Signed-off-by: Jun Zhao <mypopydev@gmail.com>
Signed-off-by: Josh de Kock <josh@itanimul.li>

fftools/cmdutils.c

@@ -1278,7 +1278,7 @@ static int show_formats_devices(void *optctx, const char *opt, const char *arg,
         const char *long_name = NULL;
 
         if (muxdemuxers !=SHOW_DEMUXERS) {
-            ifmt_opaque = NULL;
+            ofmt_opaque = NULL;
             while ((ofmt = av_muxer_iterate(&ofmt_opaque))) {
                 is_dev = is_device(ofmt->priv_class);
                 if (!is_dev && device_only)
@@ -1292,7 +1292,7 @@ static int show_formats_devices(void *optctx, const char *opt, const char *arg,
             }
         }
         if (muxdemuxers != SHOW_MUXERS) {
-            ofmt_opaque = NULL;
+            ifmt_opaque = NULL;
             while ((ifmt = av_demuxer_iterate(&ifmt_opaque))) {
                 is_dev = is_device(ifmt->priv_class);
                 if (!is_dev && device_only)