[media] dvb_usb_v2: get rid of deferred probe

Deferred probe was added in order to avoid udev vs. Kernel firmware
download problems. It is not needed anymore.
https://bugzilla.redhat.com/show_bug.cgi?id=827538

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