net/smc: cleanup listen worker mutex unlocking

For easier reading move the unlock of mutex smc_create_lgr_pending into
smc_listen_work(), i.e. into the function the mutex has been locked.
No functional change.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>