[IA64] hotplug/ia64: SN Hotplug Driver - PREEMPT/pcibus_info fix

This patch fixes an issue with the PROM and a kernel running with
CONFIG_PREEMPT enabled.  When CONFIG_PREEMPT is enabled, the size of a
spinlock_t changes -- resulting in the PROM writing to an incorrect location.

Signed-off-by: Prarit Bhargava <prarit@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>