cmake: Move cert.o to mbedtls_test_helpers library of objects

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/programs/fuzz/CMakeLists.txt b/programs/fuzz/CMakeLists.txt
index baa5ad9..57cfeee 100644
--- a/programs/fuzz/CMakeLists.txt
+++ b/programs/fuzz/CMakeLists.txt
@@ -28,7 +28,10 @@
 
 foreach(exe IN LISTS executables_no_common_c executables_with_common_c)
 
-    set(exe_sources ${exe}.c $<TARGET_OBJECTS:tf_psa_crypto_test>)
+    set(exe_sources
+        ${exe}.c
+        $<TARGET_OBJECTS:mbedtls_test_helpers>
+        $<TARGET_OBJECTS:tf_psa_crypto_test>)
     if(NOT FUZZINGENGINE_LIB)
         list(APPEND exe_sources onefile.c)
     endif()