Fix wrong axi signal in docs

[0BAB1]

I was reading through the docs and spotted a typo for the AXI signal name.

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[jquevremont]

Thanks @0BAB1 for spotting this strange mistake.

@AEzzejjari, would you be so kind as to review this small edit? This is in one of your past contributions. Thanks.

[jquevremont]

Thanks @0BAB1 @AEzzejjari :-)