aco: insert s_nop before VGPR deallocation

aco: insert s_nop before VGPR deallocation

A hazard requires this, apparently.

https://reviews.llvm.org/D155681

fossil-db (gfx1100):
Totals from 23175 (17.36% of 133461) affected shaders:
Instrs: 41240100 -> 41263275 (+0.06%)
CodeSize: 211858524 -> 211951224 (+0.04%)
Latency: 469738570 -> 469738576 (+0.00%)
InvThroughput: 58013998 -> 58013999 (+0.00%)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24320>