intel-iommu: Cope with broken HP DC7900 BIOS

intel-iommu: Cope with broken HP DC7900 BIOS

commit 0815565adfe3f4c369110c57d8ffe83caefeed68 upstream.

Yet another reason why trusting this stuff to the BIOS was a bad idea.
The HP DC7900 BIOS reports an iommu at an address which just returns all
ones, when VT-d is disabled in the BIOS.

Fix up the missing iounmap in the error paths while we're at it.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: Arto Jantunen <viiru@debian.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>