net/sched: fix retpoline wrapper compilation on configs without tc filters

Rudi reports a compilation failure on x86_64 when CONFIG_NET_CLS or
CONFIG_NET_CLS_ACT is not set but CONFIG_RETPOLINE is set.
A misplaced '#endif' was causing the issue.

Fixes: 7f0e8102

 ("net/sched: add retpoline wrapper for tc")

Tested-by: Rudi Heitbaum <rudi@heitbaum.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>