Introduce psa_key_handle_is_null inline function

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/tests/suites/test_suite_psa_crypto.function b/tests/suites/test_suite_psa_crypto.function
index 3c4d7c8..fbd7195 100644
--- a/tests/suites/test_suite_psa_crypto.function
+++ b/tests/suites/test_suite_psa_crypto.function
@@ -5761,7 +5761,7 @@
     mbedtls_free( second_export );
     psa_key_derivation_abort( &operation );
     psa_destroy_key( base_key );
-    if( handle == 0 )
+    if( psa_key_handle_is_null( handle ) )
     {
         /* In case there was a test failure after creating the persistent key
          * but while it was not open, try to re-open the persistent key