Fix memory corruption while configuring CPU windows on Marvell SoCs

Resolving CPU windows from localbus entry caused buffer overflow
and memory corruption. Fix wrong indexing and ensure the index
does not exceed table size.

Submitted by: Wojciech Macek <wma@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential revision: https://reviews.freebsd.org/D10720