pk: use better naming for the new key ID field

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/pkwrite.c b/library/pkwrite.c
index e62ad54..4bb9ac1 100644
--- a/library/pkwrite.c
+++ b/library/pkwrite.c
@@ -194,7 +194,7 @@
         }
 
         buffer_size = (size_t) (*p - start);
-        if (psa_export_public_key(key->opaque_id, start, buffer_size, &len)
+        if (psa_export_public_key(key->priv_id, start, buffer_size, &len)
             != PSA_SUCCESS) {
             return MBEDTLS_ERR_PK_BAD_INPUT_DATA;
         } else {
@@ -256,7 +256,7 @@
         psa_ecc_family_t curve;
         size_t bits;
 
-        if (PSA_SUCCESS != psa_get_key_attributes(key->opaque_id,
+        if (PSA_SUCCESS != psa_get_key_attributes(key->priv_id,
                                                   &attributes)) {
             return MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED;
         }