SDL_mixer: update vendored mpg123 again for SIZEOF_OFF_T

From 207b02b27abd18104689f343fbe00ad0137a0d76 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Tue, 9 Dec 2025 02:47:50 +0300
Subject: [PATCH] update vendored mpg123 again for SIZEOF_OFF_T

---
 external/mpg123 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/external/mpg123 b/external/mpg123
index 68b66034..57390c1c 160000
--- a/external/mpg123
+++ b/external/mpg123
@@ -1 +1 @@
-Subproject commit 68b66034fb1d72647d89cb79a0eeabc58f1ec04f
+Subproject commit 57390c1cb8419a176316c6cce002fff088bea71f