[tlul] - Update to prevent x on d_error
[tlul] - Update to prevent x on d_error

The scenario is as follows:
- A transaction is accepted (reqfifo is updated)
- reqfifo attributes are used in the next cycle to set payload such as d_error
- However, if downstream takes more than 1 cycle to return, the response during
  that cycle is unknown, and the assertion fails.

This stall is quite likely to happen in a real system, so d_error is now also
qualified with d_valid like the return data.

Signed-off-by: Timothy Chen <d7b2ae30d8c0f215facd721941273067fd1d14a2@google.com>

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