sdl12-compat: dr_mp3: disable another sint16-specific function.

SDL Commits
1 
From 1e301dd87c07fd1b97d358db6b85360d0720f2e9 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Mon, 7 Jun 2021 19:53:06 -0400
Subject: [PATCH] dr_mp3: disable another sint16-specific function.

---
 src/dr_mp3.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/dr_mp3.h b/src/dr_mp3.h
index 8f86054..20f25c2 100644
--- a/src/dr_mp3.h
+++ b/src/dr_mp3.h
@@ -3693,6 +3693,7 @@ DRMP3_API drmp3_uint64 drmp3_read_pcm_frames_f32(drmp3* pMP3, drmp3_uint64 frame
 #endif
 }
 
+#ifndef DR_MP3_NO_S16
 DRMP3_API drmp3_uint64 drmp3_read_pcm_frames_s16(drmp3* pMP3, drmp3_uint64 framesToRead, drmp3_int16* pBufferOut)
 {
     if (pMP3 == NULL || pMP3->onRead == NULL) {
@@ -3729,6 +3730,7 @@ DRMP3_API drmp3_uint64 drmp3_read_pcm_frames_s16(drmp3* pMP3, drmp3_uint64 frame
     }
 #endif
 }
+#endif
 
 static void drmp3_reset(drmp3* pMP3)
 {