vfio: platform: reset: calxedaxgmac: fix ioaddr leak

In the current code the vfio_platform_region is copied on the stack.
As a consequence the ioaddr address is not iounmapped in the vfio
platform driver (vfio_platform_regions_cleanup). The patch uses the
pointer to the region instead.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>