x86/amd-iommu: Use helper function to destroy domain

BugLink: http://bugs.launchpad.net/bugs/575853

commit 8b408fe4

 upstream.

In the amd_iommu_domain_destroy the protection_domain_free
function is partly reimplemented. The 'partly' is the bug
here because the domain is not deleted from the domain list.
This results in use-after-free errors and data-corruption.
Fix it by just using protection_domain_free instead.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Andy Whitcroft <andy.whitcroft@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>