If you create multiple vivid instances, each with their own media
device, then there was no way to tell them apart.

Fill in the bus_info so each instance has a unique bus_info string.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>