net/smc: remove device from smcd_dev_list after failed device_add()

In the Linux kernel, the following vulnerability has been resolved:

net/smc: remove device from smcd_dev_list after failed device_add()

If the device_add() for a smcd_dev fails, there's no cleanup step that

rolls back the earlier list_add(). The device subsequently gets freed,

and we end up with a corrupted list.

Add some error handling that removes the device from the list.