resources: handle overflow when aligning start of available area

resources: handle overflow when aligning start of available area

If tmp.start is near ~0, ALIGN(tmp.start) may overflow, which would
make us think there's more available space than there really is.  We
would likely return something that conflicts with a previous resource,
which would cause a failure when allocate_resource() requests the newly-
allocated region.

Reference: https://bugzilla.redhat.com/show_bug.cgi?id=646027
Reported-by: Fabrice Bellet <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Signed-off-by: Jesse Barnes <[email protected]>