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: <mesa/mesa!11954> (cherry picked from commit 9b1a2961)