aco/spill: use spills_entry instead of spills_exit to kill linear VGPRs
If a predecessor has only spilled constants (no temporaries), spills_exit
will be empty.
fossil-db (Sienna Cichlid):
Totals from 2 (0.00% of 128647) affected shaders:
Latency: 139106 -> 139104 (-0.00%)