If register_pernet_subsys success in smc_init,
we should cleanup it in case any other error.

Fixes: 64e28b52 (net/smc: add pnet table namespace support")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NUrsula Braun <ubraun@linux.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>