nir: Extract shader_info->cs.shared_size out of union.

It is valid for all stages, just 0 for most of them. In particular
mesh/task shaders might be using it.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10094>

src/intel/compiler/brw_fs.cpp

@@ -9445,7 +9445,7 @@ brw_compile_cs(const struct brw_compiler *compiler,
    const bool debug_enabled = INTEL_DEBUG & DEBUG_CS;
 
    prog_data->base.stage = MESA_SHADER_COMPUTE;
-   prog_data->base.total_shared = nir->info.cs.shared_size;
+   prog_data->base.total_shared = nir->info.shared_size;
 
    /* Generate code for all the possible SIMD variants. */
    bool generate_all;