Fix VNDK Compilation Errors

VNDK restrictions doesn't includes standard headers by
default, add them explicitly.

Change-Id: Icafac6f07fcdf58fccaabde8d472509090fb3e6f
diff --git a/hal/audio_extn/passthru.c b/hal/audio_extn/passthru.c
index f30e044..b608043 100644
--- a/hal/audio_extn/passthru.c
+++ b/hal/audio_extn/passthru.c
@@ -33,6 +33,7 @@
 #include <cutils/atomic.h>
 #include <cutils/str_parms.h>
 #include <cutils/log.h>
+#include <unistd.h>
 #include "audio_hw.h"
 #include "audio_extn.h"
 #include "platform_api.h"