PCI: Fix lock symmetry in pci_slot_unlock()

The commit a4e7728 ("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: a4e7728 ("PCI: Add missing bridge lock to pci_bus_lock()")
Signed-off-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Lukas Wunner <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Cc: [email protected]
Link: https://patch.msgid.link/[email protected]

Author: ij-intel

drivers/pci/pci.c

@@ -5542,7 +5542,8 @@ static void pci_slot_unlock(struct pci_slot *slot)
 			continue;
 		if (dev->subordinate)
 			pci_bus_unlock(dev->subordinate);
-		pci_dev_unlock(dev);
+		else
+			pci_dev_unlock(dev);
 	}
 }