iommu: Clean up release_device checks

Since .release_device is now called through per-device ops, any call
which gets as far as a driver definitely *is* for that driver, for a
device which has successfully passed .probe_device, so all the checks to
that effect are now redundant and can be removed. In the same vein we
can also skip freeing fwspecs which are now managed by core code.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/02671dbfad7a3343fc25a44222350efcb455fe3c.1655822151.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>