ac/nir: Use instance_rate_inputs per attribute, not per variable.

This did the wrong thing if we had e.g. an array for which only some
of the attributes use the instance index. Tripped up some new CTS
tests.

CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
(cherry picked from commit 5a4dc285)

Conflicts:
	src/amd/common/ac_nir_to_llvm.c