net/smc: Fix NULL pointer dereference in smc_pnet_find_ib()

[ Upstream commit d22f4f97 ]

dev_name() was called with dev.parent as argument but without to
NULL-check it before.
Solve this by checking the pointer before the call to dev_name().

Fixes: af5f60c7 ("net/smc: allow PCI IDs as ib device names in the pnet table")
Reported-by:  <syzbot+03e3e228510223dabd34@syzkaller.appspotmail.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>