V4L/DVB (5516): Reduce usbvision data size

This patch reduces usbvision driver on about 1Kb on i386 over the
original version with the old struct:
   text    data     bss     dec     hex filename
  52312   11848      60   64220    fadc old/usbvision.ko
  52474   10708      60   63242    f70a new/usbvision.ko

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