radv/rt: use terminate() when returning from raygen shaders

radv/rt: use terminate() when returning from raygen shaders

Q2RTX stats:
Totals from 7 (0.01% of 134913) affected shaders:

CodeSize: 204712 -> 204744 (+0.02%); split: -0.06%, +0.07%
Instrs: 37526 -> 37522 (-0.01%); split: -0.07%, +0.06%
Latency: 950563 -> 956024 (+0.57%)
InvThroughput: 187915 -> 188977 (+0.57%)
Copies: 4829 -> 4763 (-1.37%)
Branches: 1570 -> 1583 (+0.83%)
PreSGPRs: 407 -> 400 (-1.72%)
PreVGPRs: 614 -> 617 (+0.49%)
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21736>