Clarify "as directed here" in SSL async callback documentation
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index a839e84..606d9c2 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -624,7 +624,7 @@
  *                  propagated up the call chain. The callback should
  *                  use \c MBEDTLS_ERR_PK_xxx error codes, and <b>must not</b>
  *                  use \c MBEDTLS_ERR_SSL_xxx error codes except as
- *                  directed here.
+ *                  directed in the documentation of this callback.
  */
 typedef int mbedtls_ssl_async_sign_t( mbedtls_ssl_context *ssl,
                                       mbedtls_x509_crt *cert,
@@ -690,7 +690,7 @@
  *                  propagated up the call chain. The callback should
  *                  use \c MBEDTLS_ERR_PK_xxx error codes, and <b>must not</b>
  *                  use \c MBEDTLS_ERR_SSL_xxx error codes except as
- *                  directed here.
+ *                  directed in the documentation of this callback.
  */
 typedef int mbedtls_ssl_async_decrypt_t( mbedtls_ssl_context *ssl,
                                          mbedtls_x509_crt *cert,
@@ -738,7 +738,7 @@
  *                  The SSL handshake is aborted. The callback should
  *                  use \c MBEDTLS_ERR_PK_xxx error codes, and <b>must not</b>
  *                  use \c MBEDTLS_ERR_SSL_xxx error codes except as
- *                  directed here.
+ *                  directed in the documentation of this callback.
  */
 typedef int mbedtls_ssl_async_resume_t( mbedtls_ssl_context *ssl,
                                         unsigned char *output,