Don't use mbedtls_pk_ec in our own code

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index 14d049d..706bb70 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -287,7 +287,7 @@
                                           pk->pub_raw, pk->pub_raw_len,
                                           &pk->priv_id));
 #else
-                mbedtls_ecp_keypair *ec = mbedtls_pk_ec(*pk);
+                mbedtls_ecp_keypair *ec = mbedtls_pk_ec_rw(*pk);
                 mbedtls_mpi_free(&ec->d);
 #endif
             }