qdev: device_del: Search for to be unplugged device in 'peripheral' container

device_add puts every device with 'id' inside of 'peripheral'
container using id's value as the last component name.
Use it by replacing recursive search on sysbus with path
lookup in 'peripheral' container, which could handle both
BUS and BUS-less device cases.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>