lavf: use designated initialisers for all (de)muxers.

It's more readable and less prone to breakage.

libavformat/rmenc.c

@@ -461,15 +461,15 @@ static int rm_write_trailer(AVFormatContext *s)
 
 
 AVOutputFormat ff_rm_muxer = {
-    "rm",
-    NULL_IF_CONFIG_SMALL("RealMedia format"),
-    "application/vnd.rn-realmedia",
-    "rm,ra",
-    sizeof(RMMuxContext),
-    CODEC_ID_AC3,
-    CODEC_ID_RV10,
-    rm_write_header,
-    rm_write_packet,
-    rm_write_trailer,
+    .name              = "rm",
+    .long_name         = NULL_IF_CONFIG_SMALL("RealMedia format"),
+    .mime_type         = "application/vnd.rn-realmedia",
+    .extensions        = "rm,ra",
+    .priv_data_size    = sizeof(RMMuxContext),
+    .audio_codec       = CODEC_ID_AC3,
+    .video_codec       = CODEC_ID_RV10,
+    .write_header      = rm_write_header,
+    .write_packet      = rm_write_packet,
+    .write_trailer     = rm_write_trailer,
     .codec_tag= (const AVCodecTag* const []){ff_rm_codec_tags, 0},
 };