V4L/DVB (3819): Cxusb-bluebird: bug-fix: power down corrupts frontend

This patch prevents a bug where the frontend is unable to tune after waking
from powered down state. Now, the device remains powered on until it is
disconnected, just like the windows driver. It seems that the bluebird
firmware is unable to successfully handle tuning after a powered down state.
This patch fixes all of the FusionHDTV Bluebird USB2 devices. The Medion
MD95700 will still behave as before, since it was unaffected by this bug.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>