V4L/DVB (11187): pvrusb2: Allow sub-devices to insert correctly

A sub-device won't successfully attach to our I2C adapter if its class
isn't set to zero.  Right the class is still set to
I2C_CLASS_TV_ANALOG in order to allow the old mechanism to still
work.  This change temporarily sets the class to zero during the
interval when the sub-device attaches.  This code will get removed
when the old i2c layer is finally removed from the driver.

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