Use full internal pathname in doxygen @file directives.

Otherwise doxygen complains about ambiguous filenames when files exist
under the same name in different subdirectories.

Originally committed as revision 16912 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/truespeech.c

@@ -24,7 +24,7 @@
 
 #include "truespeech_data.h"
 /**
- * @file truespeech.c
+ * @file libavcodec/truespeech.c
  * TrueSpeech decoder.
  */