[media] dvb_usb_v2: do not release USB interface when device reconnects

USB core will call disconnect and remove driver for us as device
will disconnect itself. After that it is loaded again as a new
device but it is warm and no firmware loading needed.

Reported-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>