Add missing includes.

Change-Id: I06ea08400efa511e627be37a4fd70fbdfadea2e6
diff --git a/tools/ota/check-lost+found.c b/tools/ota/check-lost+found.c
index da02f46..cbf7926 100644
--- a/tools/ota/check-lost+found.c
+++ b/tools/ota/check-lost+found.c
@@ -26,6 +26,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <time.h>
+#include <unistd.h>
 
 #include "private/android_filesystem_config.h"