kex: Use SSH_BUFFER_FREE()

Fixes T183

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

src/kex.c

@@ -1200,9 +1200,9 @@ int ssh_make_sessionid(ssh_session session)
 
     rc = SSH_OK;
 error:
-    ssh_buffer_free(buf);
-    ssh_buffer_free(client_hash);
-    ssh_buffer_free(server_hash);
+    SSH_BUFFER_FREE(buf);
+    SSH_BUFFER_FREE(client_hash);
+    SSH_BUFFER_FREE(server_hash);
 
     session->in_hashbuf = NULL;
     session->out_hashbuf = NULL;