Fix iommu address space allocation

This fixes kernel.org bug #13584. The IOVA code attempted to optimise
the insertion of new ranges into the rbtree, with the unfortunate result
that some ranges just didn't get inserted into the tree at all. Then
those ranges would be handed out more than once, and things kind of go
downhill from there.

Introduced after 2.6.25 by ddf02886
("PCI: iova RB tree setup tweak").

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: mark gross <mgross@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>