smc: fix mutex unlocks during link group creation

Link group creation is synchronized with the smc_create_lgr_pending
lock. In smc_listen_work() this mutex is sometimes unlocked, even
though it has not been locked before. This issue will surface in
presence of the SMC rendezvous code.

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