fix: r600/sfn: variable ‘fail’ set but not used [-Wunused-but-set-variable]

Only used in debug builds.

Signed-off-by: Kai Wasserbäch <kai@dev.carbon-project.org>
Reviewed-by: Mihai Preda <mhpreda@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18643>

src/gallium/drivers/r600/sfn/sfn_scheduler.cpp

@@ -403,7 +403,7 @@ void BlockSheduler::schedule_block(Block& in_block, Shader::ShaderBlocks& out_bl
    while (collect_ready_type(exports_ready, cir.exports))
       schedule_exports(out_blocks, exports_ready);
 
-   bool fail = false;
+   ASSERTED bool fail = false;
 
    if (!cir.alu_groups.empty()) {
       std::cerr << "Unscheduled ALU groups:\n";