i2c: aspeed: disable additional device addresses on ast2[56]xx

The ast25xx and ast26xx have, respectively, two and three configurable
slave device addresses to the ast24xx's one.  We only support using
one at a time, but the others may come up in an indeterminate state
depending on hardware/bootloader behavior, so we need to make sure we
disable them so as to avoid ending up with phantom devices on the bus.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Wolfram Sang <wsa@kernel.org>