[media] cx24120: Fix hexdump length in writeregs

msg.len has been ++'d so msg.len is one too many.

Signed-off-by: Jemma Denson <jdenson@gmail.com>
Signed-off-by: Patrick Boettcher <patrick.boettcher@posteo.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>