mainboard: Fix correct index variable usage in double loop construct

Change-Id: I672c532c3f7179038d41f269bba434b8703e254b
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Found-by: Clang
Reviewed-on: http://review.coreboot.org/7718
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
4 files changed