PCI: Fix lock symmetry in pci_slot_unlock()

PCI: Fix lock symmetry in pci_slot_unlock()

The commit a4e772898f8b ("PCI: Add missing bridge lock to pci_bus_lock()")
made the lock function to call depend on dev->subordinate but left
pci_slot_unlock() unmodified creating locking asymmetry compared with
pci_slot_lock().

Because of the asymmetric lock handling, the same bridge device is unlocked
twice. First pci_bus_unlock() unlocks bus->self and then pci_slot_unlock()
will unconditionally unlock the same bridge device.

Move pci_dev_unlock() inside an else branch to match the logic in
pci_slot_lock().

Fixes: a4e772898f8b ("PCI: Add missing bridge lock to pci_bus_lock()")
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20250505115412.37628-1-ilpo.jarvinen@linux.intel.com