I recently upgraded to a 7900 XTX on Debian stable, as well. I’m running the newest kernel from Debian’s backports repo (6.6, I think), and I didn’t have that same problem.
I did have other problems with OpenCL, though. I made a thread about this and solved it with some trouble. Check my post history if you’re interested. I hope it helps. I can take a closer look at my now-working system for comparison if you have further issues.