net: ipv6: rpl_iptunnel: simplify the return expression of rpl_do_srh()

[ Upstream commit 9faad250 ]

Simplify the return expression.

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 13e55fba ("net: ipv6: fix dst ref loop on input in rpl lwt")
Signed-off-by: Sasha Levin <sashal@kernel.org>