nir/serialize: Put dest last in packed_instr::tex

packed_instr::tex::dest must be last to match the packed_instr::any::dest
position.

Fixes: 35655865cbde ("nir/serialize: pack instructions better")
Cc: stable
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17212>