r300: C&C Tiberian Sun crash with "NIR validation failed after nir_lower_locals_to_regs"

C&C3 Tiberian Sun Demo under nine crashes with NIR assertion failure in nir_lower_locals_to_regs, see the attached file for the assertion log NIR.txt. This could be related/similar to #5938 (closed) however there it is just swtcl chipset and vertex shaders, while here it looks like a fragment shader relative addressing is the problem. Old RADEON_DEBUG=use_tgsi path is broken as well, but there the issue is in the backend and I should be able to patch that soon. This is with RV530.

CC @anholt