net/smc: fix smc_buf_unuse to use the lgr pointer

The pointer to the link group is unset in the smc connection structure
right before the call to smc_buf_unuse. Provide the lgr pointer to
smc_buf_unuse explicitly.
And move the call to smc_lgr_schedule_free_work to the end of
smc_conn_free.

Fixes: a6920d1d ("net/smc: handle unregistered buffers")
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>