docs/panfrost: Fix link to use rst syntax

Hi, I'm new here. I figured I'd fix this bug as a way to introduce myself and to familiarise myself with the commit workflows. Here's hoping this isn't more trouble than it's worth reading 🙈

Currently the link uses markdown syntax to direct users to IRC, switch to rst to render this correctly.

Fixes: e3992966 ("docs/panfrost: Add web chat link")

Signed-Off by: Esme Xuan Lim esmethedev@gmail.com