V4L/DVB (11135): cx231xx: use usb_make_path() for bus_info

VIDIOC_QUERYCAP should return the proper bus info. In the case of USB, this
should be generated by usb_make_path(), being something like:
	usb-0000:00:1d.7-2

Cc: Srinivasa Deevi <srinivasa.deevi@conexant.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>