V4L/DVB (10239): pvrusb2: Fix misleading comment caused by earlier commit

Previous v4l-dvb changeset id 4cc8ed11e2e0 changed the pvrusb2-hdw
internal API regarding i2c chip debug register access.  However that
change failed to also update the corresponding function comment
describing the API.  As driver maintained I never saw a request for an
ack on that change; there probably should have been one especially
since the manner in which this API operates was changed - its
interface is now entangled with a v4l specific struct and I would have
preferred to keep this API clear of moving-target v4l-isms such as
this one if at all possible which is why I had done it the way I did
before.  But whatever.  This commit at least fixes the comment issue.

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