Merge pull request #264 from lengyijun/patch-2

Update Makefile
diff --git a/sgx_ustdc/mem.c b/sgx_ustdc/mem.c
index 3dceb03..5e4aea8 100644
--- a/sgx_ustdc/mem.c
+++ b/sgx_ustdc/mem.c
@@ -26,6 +26,7 @@
     if (error) {
         *error = ret == NULL ? errno : 0;
     }
+    return ret;
 }
 
 void u_free_ocall(void *p)