V4L/DVB (11161): pvrusb2: Set i2c autoprobing to be off by default

In order to keep a sub-device from promiscuously attaching to the
pvrusb2 driver, the i2c adapter's class must be cleared.  This change
clears that class by default.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>