We can stop trying according to try_number now and do not need to use
root_bus checking as stop sign.

In extreme case we could need to reallocate resource for device just
under root bus.  For PCI root bus hot-add, we need to retry to assign
resources to PCI devices just under pci root bus.
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>