aco/optimizer: ensure to not erase high bits when propagating packed constants

Packed constants with non-zero values in the high half
might have been propagated as 16 bit, dropping the high half.

Cc: mesa-stable
Closes: #5070
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11954>
1 file changed