nak/opt_out: fix comparison in try_combine_outs

clippy complained it was comparing the same thing

Fixes: 5b355ff25a ("nak: Fix opt_out")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27216>

src/nouveau/compiler/nak/opt_out.rs

@@ -24,7 +24,7 @@ fn try_combine_outs(emit: &mut Instr, cut: &Instr) -> bool {
         return false;
     }
 
-    if emit.stream != emit.stream {
+    if emit.stream != cut.stream {
         return false;
     }