net: sched: wrap tc_skip_wrapper with CONFIG_RETPOLINE

This patch fixes the following sparse warning:

net/sched/sch_api.c:2305:1: sparse: warning: symbol 'tc_skip_wrapper' was not declared. Should it be static?

No functional change intended.
Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
Acked-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -2302,7 +2302,9 @@ static struct pernet_operations psched_net_ops = {
 	.exit = psched_net_exit,
 };
 
+#if IS_ENABLED(CONFIG_RETPOLINE)
 DEFINE_STATIC_KEY_FALSE(tc_skip_wrapper);
+#endif
 
 static int __init pktsched_init(void)
 {