Restore accidentally-removed NULL timeout.

Change-Id: I933c80fea50950243f109acf8d6350013aaa811f
diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index 3a3df54..eddde7e 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -179,7 +179,7 @@
                 ALOG_ASSERT(coldFutexAddr != NULL);
                 int32_t old = android_atomic_dec(coldFutexAddr);
                 if (old <= 0) {
-                    (void) syscall(__NR_futex, coldFutexAddr, FUTEX_WAIT_PRIVATE, old - 1);
+                    (void) syscall(__NR_futex, coldFutexAddr, FUTEX_WAIT_PRIVATE, old - 1, NULL);
                 }
                 int policy = sched_getscheduler(0);
                 if (!(policy == SCHED_FIFO || policy == SCHED_RR)) {