media: usb: remove unnecessary (void*) conversions

No need cast (void*) to (struct dvb_usb_device *) or
(struct filter_info *).

Signed-off-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil: drop the obsolete dvb-usb/az6027.c and dvb-usb/pctv452e.c changes]