hwmon: (xgene) missing iounmap() and memunmap()

[Evgeny Novikov]

xgene_hwmon_probe() invokes ioremap() and memremap() under
certain assumptions, but the driver does not invoke iounmap() and
memunmap() either on probe error handling paths or in
xgene_hwmon_remove().

I assume a patch would be non-trivial while I have not a capability
to test it well.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Evgeny Novikov <novikov@xxxxxxxxx>