The V4L2 API requires a unique bus_info string returned as part of the
v4l2_capability structure.  These changes gather up the USB address
information, from the underlying device, into a string and report that
out through v4l2 and via sysfs (for completeness).
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>