fix benchmark error when slow

[fishautumn]

when kernel time is greater than 1s, it will failt with bellow erro:

  File "/workspace/DeepEP/tests/test_internode.py", line 205, in test_main
    t, notify_t = bench_kineto(lambda: buffer.dispatch(**tune_args), ('dispatch', 'notify'), suppress_kineto_output=True)
    ^^^^^^^^^^^
ValueError: not enough values to unpack (expected 2, got 1)