media: v4l2-dev/ioctl: require non-zero device_caps, verify sane querycap results

Now that all V4L2 drivers set device_caps in struct video_device, we can add
a check for this to ensure all future drivers fill this in.

Also verify that when the querycap ioctl is called the driver didn't mess
with the device_caps value and that capabilities is a superset of device_caps.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
[hverkuil-cisco@xs4all.nl: fix too-long line]
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>