According with the V4L2 API spec:

	"When detection is not possible or fails, the set must contain
	 all standards supported by the current video input or output."

The V4L2 core has the mask with all supported standards already. So,
apply it. Driver and subdevs can then just remove standards from the
mask, as they're able of detecting audio, video and frames frequency.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>