Add checked return to cipher setup

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/tests/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index d57e408..bff52fa 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -38,7 +38,7 @@
     (void)valid_mode; /* In some configurations this is unused */
 
     mbedtls_cipher_init( &valid_ctx );
-    mbedtls_cipher_setup( &valid_ctx, valid_info );
+    TEST_ASSERT( mbedtls_cipher_setup( &valid_ctx, valid_info ) == 0 );
     mbedtls_cipher_init( &invalid_ctx );
 
     /* mbedtls_cipher_setup() */