V4L/DVB (4736): Cx88-blackbird module is rejected during probe.

If the last cx88 board probed is not backbird based, and a previous board was,
the entire module is unloaded leading to an oops during mpeg_open on the
first /dev/videoN device.

Signed-off-by: Steven Toth <stoth@hauppauge.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>