media: uvcvideo: Fix OOB read

If the index provided by the user is bigger than the mask size, we might do
an out of bound read.

CC: stable@kernel.org
Fixes: 40140eda ("media: uvcvideo: Implement mask for V4L2_CTRL_TYPE_MENU")
Reported-by: Zubin Mithra <zsm@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>