Making the "data" argument to celt_decode() const as pointed out by Bjoern

Rasmussen.

libcelt/celt.c

@@ -911,10 +911,10 @@ static void celt_decode_lost(CELTDecoder * restrict st, celt_word16_t * restrict
 }
 
 #ifdef FIXED_POINT
-int celt_decode(CELTDecoder * restrict st, unsigned char *data, int len, celt_int16_t * restrict pcm)
+int celt_decode(CELTDecoder * restrict st, const unsigned char *data, int len, celt_int16_t * restrict pcm)
 {
 #else
-int celt_decode_float(CELTDecoder * restrict st, unsigned char *data, int len, celt_sig_t * restrict pcm)
+int celt_decode_float(CELTDecoder * restrict st, const unsigned char *data, int len, celt_sig_t * restrict pcm)
 {
 #endif
    int i, c, N, N4;
@@ -1088,7 +1088,7 @@ int celt_decode_float(CELTDecoder * restrict st, unsigned char *data, int len, c
 
 #ifdef FIXED_POINT
 #ifndef DISABLE_FLOAT_API
-int celt_decode_float(CELTDecoder * restrict st, unsigned char *data, int len, float * restrict pcm)
+int celt_decode_float(CELTDecoder * restrict st, const unsigned char *data, int len, float * restrict pcm)
 {
    int j, ret;
    const int C = CHANNELS(st->mode);
@@ -1106,7 +1106,7 @@ int celt_decode_float(CELTDecoder * restrict st, unsigned char *data, int len, f
 }
 #endif /*DISABLE_FLOAT_API*/
 #else
-int celt_decode(CELTDecoder * restrict st, unsigned char *data, int len, celt_int16_t * restrict pcm)
+int celt_decode(CELTDecoder * restrict st, const unsigned char *data, int len, celt_int16_t * restrict pcm)
 {
    int j, ret;
    VARDECL(celt_sig_t, out);

libcelt/celt.h

@@ -222,7 +222,7 @@ EXPORT void celt_decoder_destroy(CELTDecoder *st);
             returned here in float format. 
  @return Error code.
    */
-EXPORT int celt_decode_float(CELTDecoder *st, unsigned char *data, int len, float *pcm);
+EXPORT int celt_decode_float(CELTDecoder *st, const unsigned char *data, int len, float *pcm);
 
 /** Decodes a frame of audio.
  @param st Decoder state
@@ -233,7 +233,7 @@ EXPORT int celt_decode_float(CELTDecoder *st, unsigned char *data, int len, floa
             returned here in 16-bit PCM format (native endian). 
  @return Error code.
  */
-EXPORT int celt_decode(CELTDecoder *st, unsigned char *data, int len, celt_int16_t *pcm);
+EXPORT int celt_decode(CELTDecoder *st, const unsigned char *data, int len, celt_int16_t *pcm);
 
 /*  @} */