PCI: ibmphp_core.c: fix warning due to missing module_exit()

drivers/pci/hotplug/ibmphp_core.c:1414: warning: `ibmphp_exit' defined but not used

Signed-off-by: Zhenwen Xu <helight.xu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>