ACPI / hotplug / PCI: Fix reference count leak in enable_slot()

In enable_slot(), if pci_get_slot() returns NULL, we clear the SLOT_ENABLED
flag. When pci_get_slot() finds a device, it increments the device's
reference count.  In this case, we did not call pci_dev_put() to decrement
the reference count, so the memory of the device (struct pci_dev type) will
eventually leak.

Call pci_dev_put() to decrement its reference count when pci_get_slot()
returns a PCI device.

Link: https://lore.kernel.org/r/b411af88-5049-a1c6-83ac-d104a1f429be@huawei.com


Signed-off-by: Feilong Lin <linfeilong@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>