V4L/DVB (7024): usbvision: YUV to RGB conversion fixes

All YUV to RGB conversions in usbvision were reverted
(conversion to BGR but saying RGB to the application)

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>