nak: handle nop ops from NAK IR on SM50

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27178>

src/nouveau/compiler/nak/encode_sm50.rs

@@ -2103,6 +2103,7 @@ impl SM50Instr {
             Op::SuAtom(op) => si.encode_suatom(&op),
             Op::Kill(op) => si.encode_kill(&op),
             Op::CS2R(op) => si.encode_cs2r(&op),
+            Op::Nop(_) => si.encode_nop(),
             _ => panic!("Unhandled instruction {}", instr.op),
         }