radv: call lower_array_deref_of_vec before lower_io_arrays_to_elements

nir_lower_io_arrays_to_elements does not support array derefs of vectors,
even when nir_deref_instr_is_known_out_of_bounds is fixed.

They can occur with mesh shaders.

Found by inspection.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25659>