V4L/DVB (3825): Remove broken 'fast firmware load' from cx25840.

The fast firmware load hack in cx25840 uses private data. In fact, it
breaks pvrusb2 and doesn't work at all with ivtv. It is a unsafe
implementation and so it is removed.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>