eeepc-laptop: don't touch the pci slot if it was claimed by a different driver

The whole point of registering as a PCI hotplug driver was to prevent
conflict with pciehp.  At the moment it happens to work because
eeepc-laptop is loaded first, but it doesn't work the other way round.
If pciehp is loaded first then we fail to claim the slot - we need to
respect this and not handle hotplug events.

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Len Brown <len.brown@intel.com>