lavd/v4l2: use avcodec_find_decoder in list_formats

Because libavdevice/v4l2 is a demuxer, it makes sense to look for
decoders instead of encoders when listing the formats supported by the
device.
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>

libavdevice/v4l2.c

@@ -360,7 +360,7 @@ static void list_formats(AVFormatContext *ctx, int fd, int type)
                    vfd.description);
         } else if (vfd.flags & V4L2_FMT_FLAG_COMPRESSED &&
                    type & V4L_COMPFORMATS) {
-            AVCodec *codec = avcodec_find_encoder(codec_id);
+            AVCodec *codec = avcodec_find_decoder(codec_id);
             av_log(ctx, AV_LOG_INFO, "Compressed: %9s : %20s :",
                    codec ? codec->name : "Unsupported",
                    vfd.description);