usb: gadget: f_uvc: Move to video_ioctl2

Simplify ioctl handling by using video_ioctl2.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>