intel: Fix release build breakage

We missed changing one instance of debug_flag to debug_enabled in a
release-only ifdef branch.

Fixes: 758eb18c6f ("intel/compiler: Make vec4 generator take debug_enabled as a parameter")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9839>

src/intel/compiler/brw_vec4_generator.cpp

@@ -2169,7 +2169,7 @@ generate_code(struct brw_codegen *p,
 #ifndef NDEBUG
    bool validated =
 #else
-   if (unlikely(debug_flag))
+   if (unlikely(debug_enabled))
 #endif
       brw_validate_instructions(devinfo, p->store,
                                 0, p->next_insn_offset,