V4L/DVB: usbvision: add delay before detecting the saa711x

The detection of the saa711x often failed. Adding a small delay before
attempting to detect it fixed this.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>