PCI: pciehp: second try to get big range for pcie devices

Handle the case where the slot bridge that doesn't get a pre-allocated
resource big enough to handle its child resources..  For example pcie
devices need 256M, but the bridge only gets 2M preallocated.

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