Add missing #include statements.

Although Linux accepts several implicit definitions of SEEK_END found in
stdio.h, the compiler on FreeBSD won't. Rockbox compilation will fail
without stdio.h included.

There is a precedent for including this header, see
lib/rbcodec/codecs/libtremor/ivorbisfile.h.

Change-Id: I58510101b59a354cd6601cb3f323f385a824d2e8
Reviewed-on: http://gerrit.rockbox.org/639
Tested-by: Kevin Zheng <kevinz5000@gmail.com>
Reviewed-by: Frank Gevaerts <frank@gevaerts.be>

lib/rbcodec/codecs/aiff_enc.c

@@ -21,6 +21,8 @@
  ****************************************************************************/
 
 #include <inttypes.h>
+#include <stdio.h>
+
 #include "codeclib.h"
 
 CODEC_ENC_HEADER

lib/rbcodec/codecs/mp3_enc.c

@@ -34,6 +34,8 @@
 //    Library General Public License for more details.
 
 #include <inttypes.h>
+#include <stdio.h>
+
 #include "codeclib.h"
 
 CODEC_ENC_HEADER

lib/rbcodec/codecs/wav_enc.c

@@ -21,6 +21,8 @@
  ****************************************************************************/
 
 #include <inttypes.h>
+#include <stdio.h>
+
 #include "codeclib.h"
 
 CODEC_ENC_HEADER