PCI: Fix regression in pci_bus_distribute_available_resources()

The refactoring in 4292a1e45fd4 ("PCI: Refactor distributing available
memory to use loops") switched pci_bus_distribute_available_resources() to
operate on an array of bridge windows. That accidentally looked up bus
resources via pci_bus_resource_n() and then passed those pointers to helper
routines that expect the resource to belong to the device. As soon as we
execute that code, pci_resource_num() warned because the resource wasn't in
the bridge's resource array.

This happens on my AMD Strix Halo machine with Thunderbolt device; the
error message is shown below:

  WARNING: CPU: 6 PID: 272 at drivers/pci/pci.h:471 pci_bus_distribute_available_resources+0x6ad/0x6d0
  CPU: 6 UID: 0 PID: 272 Comm: irq/33-pciehp Not tainted 6.17.0+ #1 PREEMPT(voluntary)
  Hardware name: PELADN YO Series/YO1, BIOS 1.04 05/15/2025
  RIP: 0010:pci_bus_distribute_available_resources+0x6ad/0x6d0
  Call Trace:
   pci_bus_distribute_available_resources+0x590/0x6d0
   pci_bridge_distribute_available_resources+0x62/0xb0
   pci_assign_unassigned_bridge_resources+0x65/0x1b0
   pciehp_configure_device+0x92/0x160
   pciehp_handle_presence_or_link_change+0x1b5/0x350
   pciehp_ist+0x147/0x1c0

Fix the regression by always fetching the resource directly from the bridge
with pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i). This restores the
original behaviour while keeping the refactored structure.  Then we can
successfully assign resources to the Thunderbolt device.

Fixes: 4292a1e45fd4 ("PCI: Refactor distributing available memory to use loops")
Reported-by: Kenneth R. Crudup <kenny@panix.com>
Closes: https://lore.kernel.org/r/dd551b81-9e81-480b-aab3-7cf8b8bbc1d0@panix.com
Signed-off-by: Yangyu Chen <cyy@cyyself.name>
[bhelgaas: trim timestamps, etc from commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-By: Kenneth R. Crudup <kenny@panix.com>
Link: https://lore.kernel.org/r/F833CC81-7C60-48FC-A31C-B9999DCC6FA2@icloud.com
Link: https://patch.msgid.link/tencent_8C54420E1B0FF8D804C1B4651DF970716309@qq.com

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