rapidio: fix an API misues when rio_add_net() fails

rio_add_net() calls device_register() and fails when device_register()
fails. Thus, put_device() should be used rather than kfree(). Add
"mport->net = NULL;" to avoid a use after free issue.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: e8de370188d0 ("rapidio: add mport char device driver")
Signed-off-by: Haoxiang Li <[e-mail]>
Reviewed-by: Dan Carpenter <[e-mail]>
Cc: Alexandre Bounine <[e-mail]>
Cc: Matt Porter <[e-mail]>
Cc: Yang Yingliang <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/rapidio/devices/rio_mport_cdev.c

···
 		err = rio_add_net(net);
 		if (err) {
 			rmcd_debug(RDEV, "failed to register net, err=%d", err);
-			kfree(net);
+			put_device(&net->dev);
+			mport->net = NULL;
 			goto cleanup;
 		}
 	}