media: siano: fix device register error path

As reported by smatch:
	drivers/media/common/siano/smsdvb-main.c:1231 smsdvb_hotplug() warn: '&client->entry' not removed from list

If an error occur at the end of the registration logic, it won't
drop the device from the list.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/common/siano/smsdvb-main.c

@@ -1212,6 +1212,10 @@ static int smsdvb_hotplug(struct smscore_device_t *coredev,
 	return 0;
 
 media_graph_error:
+	mutex_lock(&g_smsdvb_clientslock);
+	list_del(&client->entry);
+	mutex_unlock(&g_smsdvb_clientslock);
+
 	smsdvb_debugfs_release(client);
 
 client_error: