net/smc: check for valid ib_client_data

In smc_ib_remove_dev() check if the provided ib device was actually
initialized for SMC before.

Reported-by:  <syzbot+84484ccebdd4e5451d91@syzkaller.appspotmail.com>
Fixes: a4cf0443 ("smc: introduce SMC as an IB-client")
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>