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

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>

net/smc/smc_pnet.c

@@ -311,8 +311,9 @@ static struct smc_ib_device *smc_pnet_find_ib(char *ib_name)
 	list_for_each_entry(ibdev, &smc_ib_devices.list, list) {
 		if (!strncmp(ibdev->ibdev->name, ib_name,
 			     sizeof(ibdev->ibdev->name)) ||
-		    !strncmp(dev_name(ibdev->ibdev->dev.parent), ib_name,
-			     IB_DEVICE_NAME_MAX - 1)) {
+		    (ibdev->ibdev->dev.parent &&
+		     !strncmp(dev_name(ibdev->ibdev->dev.parent), ib_name,
+			     IB_DEVICE_NAME_MAX - 1))) {
 			goto out;
 		}
 	}