decoder: Rename all main decoder plugins functions to *decoder_plugin.

src/decoder/audiofile_plugin.c

@@ -212,7 +212,7 @@ static const char *const audiofile_mime_types[] = {
 	NULL 
 };
 
-const struct decoder_plugin audiofilePlugin = {
+const struct decoder_plugin audiofile_decoder_plugin = {
 	.name = "audiofile",
 	.stream_decode = audiofile_stream_decode,
 	.tag_dup = audiofile_tag_dup,

src/decoder/ffmpeg_plugin.c

@@ -529,7 +529,7 @@ static const char *const ffmpeg_mime_types[] = {
 	NULL
 };
 
-const struct decoder_plugin ffmpeg_plugin = {
+const struct decoder_plugin ffmpeg_decoder_plugin = {
 	.name = "ffmpeg",
 	.init = ffmpeg_init,
 	.stream_decode = ffmpeg_decode,

src/decoder/modplug_plugin.c

@@ -207,7 +207,7 @@ static const char *const mod_suffixes[] = {
 	NULL
 };
 
-const struct decoder_plugin modplug_plugin = {
+const struct decoder_plugin modplug_decoder_plugin = {
 	.name = "modplug",
 	.stream_decode = mod_decode,
 	.tag_dup = mod_tagdup,

src/decoder/wavpack_plugin.c

@@ -585,7 +585,7 @@ static char const *const wavpack_mime_types[] = {
 	NULL
 };
 
-const struct decoder_plugin wavpack_plugin = {
+const struct decoder_plugin wavpack_decoder_plugin = {
 	.name = "wavpack",
 	.stream_decode = wavpack_streamdecode,
 	.file_decode = wavpack_filedecode,