MT#56471 change mix_in_fn_t indirection

Change it from a pointer type to a function signature type.

No-op.

Change-Id: I466c9141d0ea7b78b14ee9f728e7c8010b5329e5

lib/mix_buffer.c

@@ -8,12 +8,12 @@
 #include "ssrc.h"
 
 
-typedef void (*mix_in_fn_t)(void *restrict dst, const void *restrict src, unsigned int num);
+typedef void mix_in_fn_t(void *restrict dst, const void *restrict src, unsigned int num);
 
 
 struct mix_buffer_impl {
 	unsigned int sample_size;
-	mix_in_fn_t mix_in;
+	mix_in_fn_t *mix_in;
 };
 
 struct mix_buffer_ssrc_source {