vt82c686: fix coverity warning about out-of-bounds write

Refactor superio_ioport_writeb to fix the out of bounds write warning.

In addition, fix two typos: s/chage/change/

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
