radv/llvm: do not lower sub

To match ACO.

Totals from 268 (0.20% of 136420) affected shaders:
CodeSize: 1214060 -> 1214096 (+0.00%); split: -0.05%, +0.06%

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6938>
1 file changed