PCI: Remove unused assignments

Remove variables and assignments that are never used.

Found by Krzysztof using cppcheck, e.g.,

  $ cppcheck --enable=all --force
  uselessAssignmentPtrArg drivers/pci/proc.c:102 Assignment of function parameter has no effect outside the function. Did you forget dereferencing it?
  unreadVariable drivers/pci/setup-bus.c:1528 Variable 'old_flags' is assigned a value that is never used.

Reported-by: Krzysztof Wilczyński <kw@linux.com>
Link: https://lore.kernel.org/r/20220313192933.434746-2-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>