Update debug

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 4ef23f8..6fa90d4 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -1998,7 +1998,7 @@
 
     if ((ret = psa_generate_random(server_randbytes,
                                 MBEDTLS_SERVER_HELLO_RANDOM_LEN)) != 0) {
-        MBEDTLS_SSL_DEBUG_RET(1, "f_rng", ret);
+        MBEDTLS_SSL_DEBUG_RET(1, "psa_generate_random", ret);
         return ret;
     }