PCI: Do not size non-existing prefetchable window

pbus_size_mem() should only be called for bridge windows that exist but
__pci_bus_size_bridges() may point 'pref' to a resource that does not exist
(has zero flags) in case of non-root buses.

When prefetchable bridge window does not exist, the same non-prefetchable
bridge window is sized more than once which may result in duplicating
entries into the realloc_head list. Duplicated entries are shown in this
log and trigger a WARN_ON() because realloc_head had residual entries after
the resource assignment algorithm:

  pci 0000:00:03.0: [11ab:6820] type 01 class 0x060400 PCIe Root Port
  pci 0000:00:03.0: PCI bridge to [bus 00]
  pci 0000:00:03.0:   bridge window [io  0x0000-0x0fff]
  pci 0000:00:03.0:   bridge window [mem 0x00000000-0x000fffff]
  pci 0000:00:03.0: bridge window [mem 0x00200000-0x003fffff] to [bus 02] add_size 200000 add_align 200000
  pci 0000:00:03.0: bridge window [mem 0x00200000-0x003fffff] to [bus 02] add_size 200000 add_align 200000
  pci 0000:00:03.0: bridge window [mem 0xe0000000-0xe03fffff]: assigned
  pci 0000:00:03.0: PCI bridge to [bus 02]
  pci 0000:00:03.0:   bridge window [mem 0xe0000000-0xe03fffff]
  ------------[ cut here ]------------
  WARNING: CPU: 0 PID: 1 at drivers/pci/setup-bus.c:2373 pci_assign_unassigned_root_bus_resources+0x1bc/0x234

Check resource flags of 'pref' and only size the prefetchable window if the
resource has the IORESOURCE_PREFETCH flag.

Fixes: ae88d0b9 ("PCI: Use pbus_select_window_for_type() during mem window sizing")
Reported-by: Klaus Kudielka <klaus.kudielka@gmail.com>
Closes: https://lore.kernel.org/r/51e8cf1c62b8318882257d6b5a9de7fdaaecc343.camel@gmail.com/


Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Klaus Kudielka <klaus.kudielka@gmail.com>
Link: https://patch.msgid.link/20251027132423.8841-1-ilpo.jarvinen@linux.intel.com