st/mesa: fix lowered IO - don't call st_nir_assign_vs_in_locations twice

If IO is lowered, the second call is a no-op, which breaks:
   spec@!opengl 1.1@gl-1.1-color-material-unused-normal-array

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6540>
1 file changed