Add missing include of stdint.h in MIPS code.

Needed after cl https://webrtc-review.googlesource.com/c/src/+/90249,
which deleted the include of typedefs.h.

Bug: webrtc:6854
Change-Id: I4ab86fae40843613a76da378658343198a800d0c
Reviewed-on: https://webrtc-review.googlesource.com/90414
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24112}

modules/audio_coding/codecs/isac/fix/source/lattice_mips.c

@@ -9,6 +9,7 @@
  */
 
 #include <stddef.h>
+#include <stdint.h>
 
 #include "modules/audio_coding/codecs/isac/fix/source/settings.h"