If device_register() fails in cxl_register_afu|adapter(), the device
is not added, device_unregister() can not be called in the error path,
otherwise it will cause a null-ptr-deref because of removing not added
device.

As comment of device_register() says, it should use put_device() to give
up the reference in the error path. So split device_unregister() into
device_del() and put_device(), then goes to put dev when register fails.

Fixes: 14baf4d9 ("cxl: Add guest-specific code")
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Acked-by: NAndrew Donnellan <ajd@linux.ibm.com>
Acked-by: NFrederic Barrat <fbarrat@linux.ibm.com>
Link: https://lore.kernel.org/r/20221111145440.2426970-1-yangyingliang@huawei.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>