lavc: use designated initialisers for all codecs.

It's more readable and less prone to breakage.

libavcodec/gifdec.c

@@ -326,14 +326,13 @@ static av_cold int gif_decode_close(AVCodecContext *avctx)
 }
 
 AVCodec ff_gif_decoder = {
-    "gif",
-    AVMEDIA_TYPE_VIDEO,
-    CODEC_ID_GIF,
-    sizeof(GifState),
-    gif_decode_init,
-    NULL,
-    gif_decode_close,
-    gif_decode_frame,
-    CODEC_CAP_DR1,
+    .name           = "gif",
+    .type           = AVMEDIA_TYPE_VIDEO,
+    .id             = CODEC_ID_GIF,
+    .priv_data_size = sizeof(GifState),
+    .init           = gif_decode_init,
+    .close          = gif_decode_close,
+    .decode         = gif_decode_frame,
+    .capabilities   = CODEC_CAP_DR1,
     .long_name = NULL_IF_CONFIG_SMALL("GIF (Graphics Interchange Format)"),
 };