V4L/DVB (8423): cx18: remove firmware size check

This check was an ivtv leftover that served no purpose for the cx18.
Removed it, as this allows the user to load different firmware versions.

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