V4L/DVB (5729): Remove support for 256 Kb firmware files.

For backwards compatibility firmware files of 256 Kb were allowed: all
drivers have now been updated to support the newer larger firmwares so
remove this compatibility code and only support the newer firmware.

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