V4L/DVB (5530): Usbvision: remove CustomDevice facility

usbvision has a module parameter that ables the user to add a new USB 
entry at driver load. This functionality is useless by experience 
(adding statically the entry is easy). 

Furthermore, the USB_DEVICE(0xfff0, 0xfff0) USB entry caused 
usbvision_probe to be called for all unclaimed devices. 

Signed-off-by: Thierry MERLE <thierry.merle@free.fr>
Acked-by: Dwaine Garden <DwaineGarden@rogers.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>