PCI hotplug: fix ibmphp build error

Add header file to fix build error:

drivers/pci/hotplug/ibmphp_hpc.c:135: error: implicit declaration of function 'init_MUTEX'
drivers/pci/hotplug/ibmphp_hpc.c:136: error: implicit declaration of function 'init_MUTEX_LOCKED'
drivers/pci/hotplug/ibmphp_hpc.c:797: error: implicit declaration of function 'down'
drivers/pci/hotplug/ibmphp_hpc.c:807: error: implicit declaration of function 'up'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/hotplug/ibmphp_hpc.c

@@ -35,6 +35,7 @@
 #include <linux/init.h>
 #include <linux/mutex.h>
 #include <linux/sched.h>
+#include <linux/semaphore.h>
 #include <linux/kthread.h>
 #include "ibmphp.h"