macintosh/macio-adb: add missing iounmap() on error in macio_init()

Add missing iounmap(), if request_irq() fails.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230105064145.3879356-1-yangyingliang@huawei.com