cosmetics: Align muxer/demuxer declarations

Also add missing trailing commas, break long codec_tag lines and
add spaces in codec_tag declarations.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/siff.c

@@ -237,5 +237,5 @@ AVInputFormat ff_siff_demuxer = {
     .read_probe     = siff_probe,
     .read_header    = siff_read_header,
     .read_packet    = siff_read_packet,
-    .extensions = "vb,son"
+    .extensions     = "vb,son",
 };