radv: Deal with derefs from opaque types in function parameters.
Needs more copy propagation before nir_opt_derefs picks it up.
Note that the full general problem of opaque types stored in intermediate variables is still open, but that seems like a whole can of worms, and no sense to have gfxbench stay broken during the time it takes to solve that.
Cc: mesa-stable Gitlab: #5945 (closed)