net/smc: reduce smc_listen_decline() calls

smc_listen_work() contains already an smc_listen_decline() exit.
Use this exit for smc_listen_rdma_finish() problems as well.

Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>