audio: Let audio_sample_to_uint64() use const samples argument

The samples are the input to convert to u64. As we should
not modify them, mark the argument const.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200505132603.8575-2-f4bug@amsat.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

audio/audio.h

@@ -163,7 +163,7 @@ int wav_start_capture(AudioState *state, CaptureState *s, const char *path,
 bool audio_is_cleaning_up(void);
 void audio_cleanup(void);
 
-void audio_sample_to_uint64(void *samples, int pos,
+void audio_sample_to_uint64(const void *samples, int pos,
                             uint64_t *left, uint64_t *right);
 void audio_sample_from_uint64(void *samples, int pos,
                             uint64_t left, uint64_t right);

audio/mixeng.c

@@ -339,10 +339,10 @@ f_sample *mixeng_clip_float[2] = {
     clip_natural_float_from_stereo,
 };
 
-void audio_sample_to_uint64(void *samples, int pos,
+void audio_sample_to_uint64(const void *samples, int pos,
                             uint64_t *left, uint64_t *right)
 {
-    struct st_sample *sample = samples;
+    const struct st_sample *sample = samples;
     sample += pos;
 #ifdef FLOAT_MIXENG
     error_report(