Convert uses of pci_find_slot to modern API.

In the conversion sites, we end up calling pci_dev_put() right away.

This may seem like it misses the entire point of doing something like
pci_get_bus_and_slot(), since we drop the reference so soon, but it turns
out we don't actually do much with the returned pci_dev.

I plan on untangling cpqphp further, but clearly cpqphp never worried too
much about a properly refcounted pci_dev anyway. For now, this conversion
seems reasonable, as it gets rid of the last in-tree caller of pci_find_slot.
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>