glsl: use bool literals instead of integers

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12674>

src/compiler/glsl/opt_dead_builtin_varyings.cpp

@@ -527,7 +527,7 @@ lower_fragdata_array(struct gl_linked_shader *shader)
    varying_info_visitor info(ir_var_shader_out, true);
    info.get(shader->ir, 0, NULL);
 
-   replace_varyings_visitor(shader, &info, 0, 0, 0);
+   replace_varyings_visitor(shader, &info, 0, 0, false);
 }