V4L/DVB: usbvision: remove BKL from usbvision

Removed the BKL from usbvision.

There was an initialization bug as well where the i2c bus was registered twice.

Although when the BKL was present no oops was generated, I did run into
other i2c problems. Now that I protect against duplicate i2c registration
that bug is now gone as well.

But trying to disconnect the USB cable while someone is still using the device
still leads to a crash.

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