audio_extn/gef.c: Include pthread.h

* Fixes vndk build

Change-Id: I1e53e0dff91b6a001450e4dc955eadbe12aa712e
diff --git a/hal/audio_extn/gef.c b/hal/audio_extn/gef.c
index 83e9d45..4cee8ce 100644
--- a/hal/audio_extn/gef.c
+++ b/hal/audio_extn/gef.c
@@ -36,6 +36,7 @@
 #include <log/log.h>
 #include <fcntl.h>
 #include <dirent.h>
+#include <pthread.h>
 #include "audio_hw.h"
 #include "platform.h"
 #include "platform_api.h"