PCI: fix reference leak in pci_get_dev_by_id()

Alex Chiang and Matthew Wilcox pointed out that pci_get_dev_by_id() does
not properly decrement the reference on the from pointer if it is
present, like the documentation for the function states it will.

It fixes a pretty bad leak in the hotplug core (we were leaking an
entire struct pci_dev for each function of each offlined card, the first
time around; subsequent onlines/offlines were ok).

Cc: Matthew Wilcox <matthew@wil.cx>
Cc: stable <stable@kernel.org>
Tested-by: NAlex Chiang <achiang@hp.com>
Acked-by: NAlex Chiang <achiang@hp.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/search.c

@@ -280,6 +280,8 @@ static struct pci_dev *pci_get_dev_by_id(const struct pci_device_id *id,
 			      match_pci_dev_by_id);
 	if (dev)
 		pdev = to_pci_dev(dev);
+	if (from)
+		pci_dev_put(from);
 	return pdev;
 }