V4L/DVB (6336): cx8802: Plug memory leak when unregistering a driver

When a cx8802 sub-driver was unregistered, the struct cx8802_driver, which was
kmalloc()ed by cx8802_register_driver(), was deleted from the list of drivers,
but never freed.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Reviewed-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>