[media] rtl2832: rename driver state variable from 'priv' to 'dev'

Rename it device state variable to dev. Both priv and dev are very
common terms for such variable in kernel, but I like use dev in
order to keep drivers consistent.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>