r300: tweak nir loop unrolling hint for r500 vertex shaders
This should prevent some cxbx-r shaders from unrolling above the instruction limit and results in 3 gained cxbx-r shaders on RV530 with no other changes in shader-db. Closes: mesa/mesa#5967 Signed-off-by:Pavel Ondračka <pavel.ondracka@gmail.com> Reviewed-by:
Filip Gawin <filip@gawin.net> Part-of: <mesa/mesa!19702>