PCI: don't shrink bridge resources

When clearing leaf bridge resources, trying to get a big enough one, we
could shrink the bridge if there is no resource under it.  Confirm
against the old resource side to make sure we're increasing the
allocation.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>