nak: sm50: fix ineg legalization

There is nothing to be done, as we lower this op unconditionally.

We need to add an arm in the match to not panic, though.

Fixes a panic in
dEQP-VK.binding_model.shader_access.primary_cmd_buf.sampler_immutable.vertex_fragment.multiple_contiguous_descriptors.2d

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26587>

src/nouveau/compiler/nak/legalize.rs

@@ -324,6 +324,7 @@ fn legalize_sm50_instr(
         }
         Op::Ldc(_) => (),  // Nothing to do
         Op::Copy(_) => (), // Nothing to do
+        Op::INeg(_) => (), /* we unconditionally lower this */
         _ => {
             let src_types = instr.src_types();
             for (i, src) in instr.srcs_mut().iter_mut().enumerate() {