[media] nuvoton-cir: fix setting ioport base address

[media] nuvoton-cir: fix setting ioport base address

At least on Zotac CI321 ACPI provides an ioport range for the wake up part
but accessing these ioports has no effect.
Instead the ioport base address is set to another value already
(0xa20 in my case) and accessing this ioport range works.

Therefore set a new ioport base address only if the current ioport base
address is 0 (register reset default).

The need to use the existing base address instead of trying to set
an own one doesn't seem to be limited to this specific device as other
drivers like hwmon/nct6775 do it the same way.

This change was successfully tested on the mentioned device.
And the change should be generic enough to not break the driver for
other chips (however due to lack of appropriate hardware I wasn't
able to test this).

[mchehab@osg.samsung.com: Tested on Intel NUC NUC5i7RYB with BIOS
 version RYBDWi35.86A.0350.2015.0812.1722]

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>