blackfin: cplb-nompu: fix ROM cplb size for bf609-ezkit

In user xip test, there is a cplb error when ROMKERNEL try to mount romfs
using 'mount -t romfs /dev/mtdblock2 /mnt', becasue the CPLB setting is not
correct.

Signed-off-by: Bob Liu <lliubbo@gmail.com>