media: uvcvideo: Constify formats, frames and intervals

The formats, frames and intervals stored in the uvc_streaming structure
are not meant to change after being parsed at probe time. Make them
const to prevent unintended modifications, and adapt the probe code
accordingly to use non-const pointers during parsing.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>