PCI: Move __pci_walk_bus() mutex to where we need it

PCI: Move __pci_walk_bus() mutex to where we need it

Simplify __pci_walk_bus() by moving the pci_bus_sem mutex into
pci_walk_bus(), the only place it is needed, and removing the parameter
that told __pci_walk_bus() whether to acquire the mutex.

Link: https://lore.kernel.org/r/20241022224851.340648-4-kbusch@meta.com
Signed-off-by: Keith Busch <kbusch@kernel.org>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>