pk: use better naming for the new key ID field

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/src/test_helpers/ssl_helpers.c b/tests/src/test_helpers/ssl_helpers.c
index 23f5977..fbf9ea5 100644
--- a/tests/src/test_helpers/ssl_helpers.c
+++ b/tests/src/test_helpers/ssl_helpers.c
@@ -595,7 +595,7 @@
         if (cert->pkey != NULL) {
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
             if (mbedtls_pk_get_type(cert->pkey) == MBEDTLS_PK_OPAQUE) {
-                psa_destroy_key(cert->pkey->opaque_id);
+                psa_destroy_key(cert->pkey->priv_id);
             }
 #endif
             mbedtls_pk_free(cert->pkey);