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>