Pynvml declaration fix

Hi,

I think nvmlDeviceGetMinMaxFanSpeed should be changed from:

def nvmlDeviceGetMinMaxFanSpeed(handle, minSpeed, maxSpeed):
    fn = _nvmlGetFunctionPointer("nvmlDeviceGetMinMaxFanSpeed")
    ret = fn(handle, minSpeed, maxSpeed)
    _nvmlCheckReturn(ret)
    return ret

to:

def nvmlDeviceGetMinMaxFanSpeed(handle):
  c_minSpeed = c_uint()
  c_maxSpeed = c_uint()
  fn = _nvmlGetFunctionPointer("nvmlDeviceGetMinMaxFanSpeed")
  ret = fn(handle, byref(c_minSpeed), byref(c_maxSpeed))
  _nvmlCheckReturn(ret)
  return c_minSpeed.value, c_maxSpeed.value