nir/search: support swizzles on expressions in replacement patterns

Before this wasn't a compile time error, but it also didn't do anything.

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36117>

src/compiler/nir/nir_search.c

@@ -500,7 +500,10 @@ construct_value(nir_builder *build,
 
       nir_alu_src val;
       val.src = nir_src_for_ssa(&alu->def);
-      memcpy(val.swizzle, identity_swizzle, sizeof val.swizzle);
+      if (expr->swizzle < 0)
+         memcpy(val.swizzle, identity_swizzle, sizeof(val.swizzle));
+      else
+         memset(val.swizzle, expr->swizzle, sizeof(val.swizzle));
 
       return val;
    }