coreaudio: fix sloppy "posixification" by 1ea879e5

#ifdef FLOAT_MIXENG

typedef float mixeng_real;

struct mixeng_volume { int mute; mixeng_real r; mixeng_real l; };

struct mixeng_sample { mixeng_real l; mixeng_real r; };

struct st_sample { mixeng_real l; mixeng_real r; };

#else

struct mixeng_volume { int mute; int64_t r; int64_t l; };

struct st_sample { int64_t l; int64_t r; };