PCI: Fix premature removal from realloc_head list during resource assignment

reassign_resources_sorted() checks for two things:

a) Resource assignment failures for mandatory resources by checking if the
resource remains unassigned, which are known to always repeat, and does
not attempt to assign them again.

b) That resource is not among the ones being processed/assigned at this
stage, leading to skip processing such resources in
reassign_resources_sorted() as well (resource assignment progresses
one PCI hierarchy level at a time).

The problem here is that a) is checked before b), but b) also implies the
resource is not being assigned yet, making also a) true. As a) only skips
resource assignment but still removes the resource from realloc_head, the
later stages that would need to process the information in realloc_head
cannot obtain the optional size information anymore. This leads to
considering only non-optional part for bridge windows deeper in the PCI
hierarchy.

This problem has been observed during rescan (add_size is not considered
while attempting assignment for 0000:e2:00.0 indicating the corresponding
entry was removed from realloc_head while processing resource assignments
for 0000:e1):

pci_bus 0000:e1: scanning bus
...
pci 0000:e3:01.0: bridge window [mem 0x800000000-0x1000ffffff 64bit pref] to [bus e4] add_size 60c000000 add_align 800000000
pci 0000:e3:01.0: bridge window [mem 0x00100000-0x000fffff] to [bus e4] add_size 200000 add_align 200000
pci 0000:e3:02.0: disabling bridge window [mem 0x00000000-0x000fffff 64bit pref] to [bus e5] (unused)
pci 0000:e2:00.0: bridge window [mem 0x800000000-0x1000ffffff 64bit pref] to [bus e3-e5] add_size 60c000000 add_align 800000000
pci 0000:e2:00.0: bridge window [mem 0x00100000-0x001fffff] to [bus e3-e5] add_size 200000 add_align 200000
pcieport 0000:e1:02.0: bridge window [io size 0x2000]: can't assign; no space
pcieport 0000:e1:02.0: bridge window [io size 0x2000]: failed to assign
pcieport 0000:e1:02.0: bridge window [io 0x1000-0x2fff]: resource restored
pcieport 0000:e1:02.0: bridge window [io 0x1000-0x2fff]: resource restored
pcieport 0000:e1:02.0: bridge window [io size 0x2000]: can't assign; no space
pcieport 0000:e1:02.0: bridge window [io size 0x2000]: failed to assign
pci 0000:e2:00.0: bridge window [mem 0x28f000000000-0x28f800ffffff 64bit pref]: assigned

Fixes: 96336ec70264 ("PCI: Perform reset_resource() and build fail list in sync")
Reported-by: Peter Nisbet <peter.nisbet@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Peter Nisbet <peter.nisbet@intel.com>
Link: https://patch.msgid.link/20260313084551.1934-1-ilpo.jarvinen@linux.intel.com