iommu/virtio: Do not dereference fwnode in struct device

In order to make the underneath API easier to change in the future,
prevent users from dereferencing fwnode from struct device.
Instead, use the specific device_match_fwnode() API for that.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20220801165142.20898-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>