[media] pvrusb2: replace .ioctl by .unlocked_ioctl

As far as I can tell pvrusb2 does its own locking, so there is
no need to use .ioctl.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>