Add missed intermediate file

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 2428818..eff44d8 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -379,6 +379,7 @@
 
 cli2.req.sha256: cli2.key
 	$(MBEDTLS_CERT_REQ) output_file=$@ filename=$< subject_name="C=NL,O=PolarSSL,CN=PolarSSL Test Client 2" md=SHA256
+all_intermediate += cli2.req.sha256
 
 all_final += server1.req.sha1
 cli2.crt: cli2.req.sha256